Porous, crystallized, aromatic polycarbonate prepolymer, a porous, crystallized aromatic polycarbonate, and production methods

ABSTRACT

A porous, crystallized, aromatic polycarbonate prepolymer is disclosed, which comprises recurring aromatic carbonate units and terminal hydroxyl and aryl carbonate groups, wherein these terminal groups are in a specific molar ratio, and has specific number average molecular weight, surface area and crystallinity. The prepolymer can readily be converted by solid-state condensation polymerization to a porous, crystallized, aromatic polycarbonate having excellent properties. The porous, crystallized, aromatic polycarbonate of the present invention can readily be molded to obtain a shaped, porous, crystallized polycarbonate. The porous, crystallized, aromatic polycarbonate and the shaped, porous, crystallized polycarbonate of the present invention have excellent heat resistance and solvent resistance and exhibit advantageously low water absorption so that these are suited for use as a filter material, an adsorbent or the like. The porous, crystallized, aromatic polycarbonate and the shaped porous, crystallized polycarbonate of the present invention can also readily be molded by a melt process into an article useful as engineering plastics, such as an optical element and an electronic component, which is appreciated since it is free of impurities, such as chlorine-containing compounds, and has excellent properties.

TECHNICAL FIELD

The present invention relates to a porous, crystallized, aromaticpolycarbonate prepolymer, a porous, crystallized aromatic polycarbonate,and production methods therefor. More particularly, the presentinvention is concerned with a porous, crystallized, aromaticpolycarbonate prepolymer having terminal hydroxyl and aryl carbonategroups in a specific molar ratio and having a specific number averagemolecular weight, surface area and crystallinity, which can readily beconverted by solid-state condensation polymerization to a porous,crystallized aromatic polycarbonate having excellent properties. Theporous, crystallized aromatic polycarbonate of the present invention canreadily be molded to obtain a shaped, porous, crystallizedpolycarbonate. The porous, crystallized aromatic polycarbonate and theshaped, porous, crystallized polycarbonate of the present invention haveexcellent heat resistance and solvent resistance and exhibitadvantageously low water absorption so that they are suited for use as afilter material or an adsorbent. The porous, crystallized aromaticpolycarbonate and the shaped porous, crystallized polycarbonate of thepresent invention can also be readily molded by a melt process into anarticle useful as engineering plastics, such as an optical element andan electronic component, which is appreciated since it is free ofimpurities, such as chlorine-containing compounds, and has excellentproperties.

BACKGROUND ART

In recent years, aromatic polycarbonates have been widely employed invarious fields as engineering plastics which have excellent heatresistance, impact resistance and transparency. Various studies havebeen made with respect to processes for producing aromaticpolycarbonates. Up to now processes, such as one utilizing interfacialcondensation polymerization of an aromatic dihydroxy compound, such as2,2-bis(4-hydroxyphenyl)propane (hereinafter frequently referred to as"bisphenol A"), with phosgene (hereinafter frequently referred to as the"phosgene process"), have been commercially practiced. In the phosgeneprocess, a mixed solvent of water or an aqueous alkali solution and awater-immiscible organic solvent are generally used. Commercially, amixed solvent of an aqueous sodium hydroxide solution and methylenechloride are employed. As a catalyst for polymerization, a tertiaryamine or a quaternary ammonium compound is employed. By-producedhydrogen chloride is removed as a salt with a base.

However, in the interfacial condensation polymerization processemploying phosgene, (1) toxic phosgene must be used; (2) due to theby-produced chlorine-containing compounds, such as hydrogen chloride andsodium chloride, the apparatus used is likely to be corroded; (3) it isdifficult to remove impurities which adversely influence the polymerproperties, such as sodium chloride, from the polymer; and (4) sincemethylene chloride (which is generally used as a reaction solvent) is agood solvent for polycarbonate and has a strong affinity topolycarbonate, methylene chloride inevitably remains in producedpolycarbonate. Removal of the remaining methylene chloride on acommercial scale is extremely costly, and complete removal of theremaining methylene chloride from the obtained polycarbonate is almostimpossible. Further, it is noted that the methylene chloride remainingin the polymer is likely to be decomposed, e.g., by heat at the time ofmolding, thereby forming hydrogen chloride, which not only causescorrosion of a molding machine but also lowers the quality of thepolymer. Furthermore, when it is intended to produce a polycarbonatehaving a high molecular weight (e.g., number average molecular weight of15,000 or more), a methylene chloride solution of such a polycarbonatehas an extremely high viscosity, thereby making agitation of thesolution difficult. Additionally, sticky polymer solution is produced,and hence it becomes extremely difficult to separate the polymer frommethylene chloride. Therefore, commercial production of a high quality,high molecular weight polycarbonate by the phosgene process is extremelydifficult.

As mentioned above, the phosgene process involves too many problems tobe practiced commercially.

Meanwhile, various methods are known in which an aromatic polycarbonateis produced from an aromatic dihydroxy compound and a diaryl carbonate.For example, a process, which is generally known as atransesterification process or a melt process, is commerciallypracticed. In this process, a polycarbonate is produced by performing amolten-state ester exchange reaction between bisphenol A and diphenylcarbonate in the presence of a catalyst, while effecting elimination ofphenol. However, in order to attain the desired polymerization degree ofthe final aromatic polycarbonate according to this process, phenol and,finally, diphenyl carbonate need to be distilled off from a formedmolten polycarbonate of high viscosity (e.g., 8,000 to 20,000 poise at280° C.), and it is generally necessary to perform the reaction at atemperature as high as 280° to 310° C. in vacuo as high as 1 mmHg orless for a period of time as long as, e.g., 4 to 5 hours. Therefore,this process has many disadvantages. For example, (1) both specialapparatus (suitable for reaction at high temperatures and under highvacuum) and a special stirrer of great power (useful under the highviscosity conditions of the product to be formed) are needed; (2) due tothe high viscosity of the product, when a reactor or stirring typereactor (which is usually employed in the plastic industry) is used,only a polymer having a weight average molecular weight as low as about30,000 is obtained; (3) due to the high temperature at which thereaction is performed, branching and crosslinking of the polymer arelikely to occur, thereby rendering it difficult to obtain a polymer ofgood quality; and (4) due to long residence time at high temperatures,discoloration of the polymer is likely to occur [see Mikio Matsukane etal, Purasuchikku Zairyo Koza 5 "Porikaboneito Jushi" (Seminar on PlasticMaterials 5, "Polycarbonate Resin"), Nikkan Kogyo Shinbun PublishingCo., p.62-67, Japan (1969)].

Moreover, with respect to the polycarbonate obtained by the meltprocess, it is known that the molecular weight distribution of thepolymer is broad, and that the proportion of branched structure is high.Therefore, it is recognized that the polycarbonate produced by the meltprocess is inferior to that produced by the phosgene process inproperties, such as mechanical strength, and that, particularly, thepolycarbonate produced by the melt process is disadvantageous because ofits brittle fracture properties, and it is also poor in moldabilitybecause of its non-Newtonian flow behavior [see Mikio Matsukane,"Kobunshi" (High Polymer), Japan, Vol. 27, p.521 (1978)].

Meanwhile, in the production of polyhexamethylene adipamide (nylon 66)and polyethylene terephthalate (PET), which are examples of the mostpopular condensation polymerized polymers, polymerization is generallyconducted by a melt polymerization process until the polymer has amolecular weight at which mechanical properties sufficient for a plasticor a fiber are exhibited. With respect to this production, it is knownthat the polymerization degree of the thus produced polymer can befurther increased by solid-state condensation polymerization in whichthe polymer is heated at a temperature (at which the polymer can remainin solid-state) at a reduced pressure or atmospheric pressure under astream of, e.g., dry nitrogen. In this polymerization, it is believedthat dehydration condensation is advanced in the solid polymer by thereaction of terminal carboxyl groups with adjacent terminal amino groupsor terminal hydroxyl groups. Also, in the case of polyethyleneterephthalate, condensation reaction by the elimination of ethyleneglycol from the formed polymer occurs to some extent simultaneously witha condensation reaction between functional groups.

The reason why the polymerization degree of nylon 66 and polyethyleneterephthate can be increased by solid-state condensation polymerizationis that these polymers are inherently crystalline polymers having a highmelting point (e.g., 265° C. and 260° C.) and, hence, these polymers canremain sufficiently in solid-state at a temperature at which solid-statepolymerization proceeds (e.g., 230° C. to 250° C.). What is moreimportant is that, for the above-mentioned polymers, the compounds to beeliminated are substances, such as water and ethylene glycol, that havea low molecular weight and relatively low boiling point and, therefore,can readily move within and through the solid polymer so that they canbe removed from the reaction system as gases.

On the other hand, it has been proposed to employ a method for producingan aromatic polyester carbonate having a high molecular weight in whicha high melting temperature aromatic polyester carbonate having both anaromatic ester bond and an aromatic carbonate bond is subjected to meltpolymerization, and then subjected to solid-state condensationpolymerization. According to this method, an aromatic dicarboxylic acidor aromatic oxycarboxylic acid, such as naphthalene dicarboxylic acid,p-hydroxybenzoic acid or terephthalic acid, is reacted with an aromaticdihydroxy compound and a diaryl carbonate in their molten state toprepare a prepolymer. Then, the prepolymer is crystallized and subjectedto solid-state condensation polymerization. If the polymerization degreeis increased to some extent by melt polymerization at 260° to 280° C.,when p-hydroxybenzoic acid is used, the resultant product is no longerin a molten state but becomes solid. Since the resultant solid is aprepolymer having high crystallinity and a high melting temperature, itis not necessary to crystallize the solid further (see Japanese PatentApplication Laid-Open Specification No. 48-22593, Japanese PatentApplication Laid-Open Specification No. 49-31796, U.S. Pat. No.4,107,143, Japanese Patent Application Laid-Open Specification No.55-98224). However, these methods apply only to the production of anaromatic polyester carbonate containing 30% or more, generally 50% ormore, of ester bonds, and it has been reported that, although anaromatic polyester carbonate containing less than 30 % of ester bondswas intended to be produced, fusion of a prepolymer occurred at the timeof solid-state polymerization so that the solid-state condensationpolymerization could not be conducted (Japanese Patent ApplicationLaid-Open Specification No. 55-98224).

On the other hand, it is known that the presence of ester bonds asmentioned above promotes the carbonate bond-forming reaction when anaromatic polyester carbonate is produced by a melt condensationpolymerization method (see Japanese Patent Application PublicationSpecification No. 52-36797). According to the Japanese PatentApplication Publication Specification No 52-36797, when a high molecularweight aromatic polycarbonate having ester bonds is produced by meltcondensation polymerization, the melt condensation polymerizationreaction is markedly promoted by introducing ester bonds, in advance,into the molecular chain of an aromatic polycarbonate having a lowpolymerization degree. Naturally, it is believed that theabove-mentioned effect of promoting the condensation polymerizationreaction by the ester bonds may also be exhibited at the time ofsolid-state condensation polymerization. Therefore, it is relativelyfacile to increase the polymerization degree by solid-state condensationpolymerization with respect to an inherently crystalline aromaticpolyester carbonate having a high melting temperature, for example, apolymer having 40 mole % of ester bonds obtained from p-hydroxybenzoicacid, hydroquinone and diphenyl carbonate, or an aromatic polyestercarbonate (such as a polymer having 55 mole % of ester bonds obtainedfrom 2,6-naphthalene dicarboxylic acid, bisphenol A and diphenylcarbonate) which can easily become a crystalline polymer having a highmelting temperature, by a simple crystallizing operation, for example,by heating at a predetermined temperature lower than the meltingtemperature.

However, no attempt has been made by any persons skilled in the artother than the group of the present inventors to produce a highmolecular weight aromatic polycarbonate containing no ester bond by amethod in which a prepolymer having a low molecular weight is firstprepared by melt polymerization, and then the polymerization degree ofthe prepolymer is increased by solid-state condensation polymerization,except for the case where a specific highly crystalline polycarbonatehaving a melting temperature as high as 280° C. or more has beenproduced by solid-state condensation polymerization (see Example 3 ofJapanese Patent Application Laid-open Specification No. 52-109591).Japanese Patent Application Laid-open Specification No. 52-109591discloses a method in which melt polymerization of an aromatic dihydroxycompound comprising about 70% of hydroquinone and about 30% of bisphenolA with diphenyl carbonate is conducted at 280° C. under an extremelyreduced pressure, i.e., 0.5 mmHg, to form a solidified prepolymer havinga melting temperature of more than 280° C., and then the polymerizationdegree of the prepolymer is increased by solid-state condensationpolymerization at 280° C. under 0.5 mmHg for 4 hours.

However, with respect to a substantially amorphous aromaticpolycarbonate comprised mainly of a dihydroxydiaryl alkane, such asbisphenol A, no noteworthy attempt has been made by any persons skilledin the art other than the group of the present inventors to produce apolymer having a high molecular weight by first forming a prepolymerhaving a relatively low molecular weight and then subjecting theprepolymer to solid-state condensation polymerization. For example, inthe phosgene process using an acid acceptor, which is the mostrepresentative method for producing an aromatic polycarbonate, since acompound, such as sodium chloride, to be removed from the reactionsystem to advance the condensation reaction is generally solid in theabsence of a solvent, the compound hardly moves within and through thesolid polymer. Therefore, it is difficult to remove the compound fromthe reaction system. It is thus not feasible to carry out this methodusing phosgene in a solid state condensation system.

With respect to a method for producing the most popular aromaticpolycarbonate, i.e., a polycarbonate derived from bisphenol A bytransesterification between bisphenol A and diphenyl carbonate, all ofthe studies have been directed toward a melt polymerization process athigh temperature under highly reduced pressure. Studies of other personsskilled in the art any than the group of the present inventors havenever been directed toward a method in which a prepolymer having arelatively low polymerization degree is first prepared, and then thepolymerization degree of the prepolymer is increased by solid-statecondensation polymerization to obtain a polycarbonate having a highmolecular weight. Because polycarbonates derived from bisphenol A areamorphous polymers having a glass transition temperature (Tg) of from149° to 150° C., it has been considered to be infeasible to subjectpolycarbonates derived from bisphenol A to solid-state condensationpolymerization. In other words, in order for a prepolymer to besusceptible to solid-state condensation polymerization, it is generallyrequired that the prepolymer not be fused but maintain its solid-stateat a temperature higher than the glass transition temperature of theprepolymer (if the temperature is lower than the glass transitiontemperature of the prepolymer, molecular motion does not occur, thusprecluding solid-state condensation polymerization). Amorphouspolycarbonate which melts at a temperature of 150° C. or more ispractically not susceptible to solid-state condensation polymerization.

The only proposals hitherto made for producing an aromatic polycarbonatecomprised mainly of a dihydroxydiaryl alkane, such as bisphenol A, whichis a substantially amorphous polymer, by solid-state condensationpolymerization, are those disclosed by the group of the presentinventors in Japanese Patent Application Laid-Open Specifications No.63-223035, No. 64-1725, No. 64-4617, No. 64-16826 and No. 64-16827.

Japanese Patent Application Laid-Open Specifications No. 63-223035 andNo. 64-4617 disclose that solid-state condensation polymerization can beeffected in the production of a polycarbonate of bisphenol A by selfcondensation reaction of a bisalkyl carbonate of an aromatic dihydroxycompound, e.g., bis(methyl carbonate) of bisphenol A represented by theformula: ##STR1## in which dimethyl carbonate groups are removed at anelevated temperature. In particular, in the methods of Japanese PatentApplication Laid-Open Specifications No. 63-223035 and No. 64-4617,pre-polymerization is performed to obtain a prepolymer having methylcarbonate groups at both terminals thereof which is represented by theformula: ##STR2## wherein l is an integer of from 2 to about 30, theprepolymer is subjected to solvent or heating treatment for effectuatingcrystallization of the prepolymer, and then solid-state condensationpolymerization is performed.

On the other hand, Japanese Patent Application Laid-Open SpecificationsNo. 64-1725, No. 64-16826 and No. 64-16827 disclose that a polycarbonateof bisphenol A can be produced by reacting, for example, bis(methylcarbonate) of bisphenol A represented by formula (I) with diphenylcarbonate to produce a prepolymer having a methyl carbonate group and aphenyl carbonate group as terminal groups [such as that represented bythe formula: ##STR3## wherein l is as defined above], and subjecting theprepolymer to solvent or heating treatment for crystallizing theprepolymer and then to solid-state condensation polymerization. In themethods of these patent application laid-open specifications, asdifferent from the methods of Japanese Patent Application Laid-OpenSpecifications No. 63-223035 and No. 64-4617, condensationpolymerization is advanced by elimination reaction of methyl phenylcarbonate from the terminal methyl carbonate and phenyl carbonategroups.

Generally, in solid-state condensation polymerization, thepolymerization temperature can be low as compared to that inmolten-state polymerization. Accordingly, a major advantage of asolid-state polymerization method resides in that the thermaldegradation of a polymer during the polymerization step is suppressed,and that hence a high quality polymer is obtained. However, thesolid-state condensation polymerization has a grave drawback in that thepolymerization rate is low. In the method of producing an aromaticpolycarbonate through solid-state condensation polymerization which isaccompanied by the above-mentioned elimination reaction of dimethylcarbonate or methyl phenyl carbonate groups as well, the polymerizationrate is not sufficiently high and hence a prolonged polymerization timehas been necessary. A catalyst can be used to increase thepolymerization rate in solid-state condensation polymerization. However,the catalyst is likely to remain in the final polymer, and hence the useof a catalyst is likely to cause a problem of quality degradation offinal polymers (e.g., occurrence of silver streaks on the surface of ashaped article of polymers).

DISCLOSURE OF THE INVENTION

The present inventors previously found that solid-state condensationpolymerization could be effectively performed to increase the molecularweight of formed polycarbonate in the production of an aromaticpolycarbonate from, as starting materials, a dihydroxyaryl compoundcomposed mainly of a dihydroxydiaryl alkane, such as bisphenol A, and adiaryl carbonate, such as diphenyl carbonate, and filed patentapplications (Japanese Patent Application No. 63-240785, InternationalPatent Application No. PCT/JP88/00989 and Japanese Patent ApplicationNo. 63-327678). These applications disclose methods for producing a highquality aromatic polycarbonate in which a substantially amorphousprepolymer having hydroxyl and aryl carbonate groups as terminal groupsis crystallized and then subjected to solid-state condensationpolymerization, and the inventions of the applications are based on anunexpected finding that the crystallinity of a prepolymer plays animportant role in the practice of solid-state condensationpolymerization.

Ever since, the present inventors have continued studies with respect toan improved method for producing an aromatic polycarbonate bysolid-state condensation polymerization. As a result, unexpectedly, thepresent inventors have found that the specific surface area of acrystallized aromatic polycarbonate prepolymer exerts a marked influenceupon the practice of solid-state condensation polymerization. Further,the present inventors have unexpectedly found that a porous,crystallized aromatic polycarbonate prepolymer having terminal hydroxyland aryl carbonate groups in a specific molar ratio and having specificnumber average molecular weight, specific surface area and crystallinitycan readily be converted by solid-state condensation polymerization to aporous, crystallized, aromatic polycarbonate having excellentproperties. Based on these unexpected findings, the present inventionhas been completed.

Accordingly, it is an object of the present invention to provide aporous, crystallized aromatic polycarbonate prepolymer which can readilybe converted by solid-state condensation polymerization to a porous,crystallized, aromatic polycarbonate having excellent properties.

It is another object of the present invention to provide an efficientmethod for producing the above-mentioned prepolymer.

It is a further object of the present invention to provide a porous,crystallized, aromatic polycarbonate and a shaped, porous, crystallizedpolycarbonate having excellent heat resistance and solvent resistance,exhibiting advantageously low water absorption and being free ofimpurities.

It is still a further object of the present invention to provide anefficient method for producing each of the above-mentioned porous,crystallized, aromatic polycarbonate and shaped, porous, crystallized,aromatic polycarbonate.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andappended claims taken in connection with the accompanying drawings.

In one aspect of the present invention, there is provided a porous,crystallized, aromatic polycarbonate prepolymer comprising recurringaromatic carbonate units and terminal hydroxyl and aryl carbonategroups, wherein the molar ratio of the terminal hydroxyl groups to theterminal aryl carbonate groups is from 5/95 to 95/5, and having a numberaverage molecular weight of from 1,000 to 15,000, a specific surfacearea of at least 0.2 m² /g and a crystallinity of at least 5%.

The porous, crystallized, aromatic polycarbonate prepolymer of thepresent invention comprises recurring aromatic carbonate unitsrepresented by formula (IV): ##STR4## wherein Ar is a divalent aromaticgroup, and terminal hydroxyl and aryl carbonate groups. The terminalhydroxyl group (--OH) is directly bonded to the aromatic group. Theterminal aryl carbonate group is represented by formula (V): ##STR5##wherein Ar³ is a monovalent aromatic group. The molar ratio of theseterminal groups of the prepolymer is not specifically restricted andvaried according to the number average molecular weight of theprepolymer, the properties of an aromatic polycarbonate intended to beproduced from the prepolymer, and the like. Generally, the molar ratioof ##STR6## is within the range of from 5/95 to 95/5, preferably from10/90 to 90/10, more preferably 20/80 to 80/20.

With respect to the molar ratio of the terminal groups of theprepolymer, an explanation is given below, referring to a prepolymerhaving a number average molecular weight of 4,000. When a ultra-highmolecular weight aromatic polycarbonate having a molecular weight of,for example, 15,000 or more is intended to be produced from theprepolymer, it is preferred that the molar ratio of ##STR7## of theprepolymer be within the range of from 40/60 to 60/40, because a highpolymerization rate can be attained. Production of the ultra-highmolecular weight aromatic polycarbonate by the conventional phosgeneprocess or melt process (transesterification process) is extremelydifficult or impossible because the viscosity of the polymerizationreaction mixture is rapidly increased before the intended ultra-highmolecular weight aromatic polycarbonate is produced. However, by themethod of the present invention, a prepolymer having the above-mentionedvalue of number average molecular weight and a molar ratio of theterminal groups within the above-mentioned range can be polymerizedwithout being subjected to any influence of the viscosity of thereaction mixture. Therefore, by the use of the above prepolymer of thepresent invention, an ultra-high molecular weight aromatic polycarbonatecan advantageously be produced. When it is intended to produce anaromatic polycarbonate (number average molecular weight of 6,000 to13,000) to be used for injection molding or for extrusion molding, it ispreferred that the amount of the terminal hydroxyl groups of theprepolymer be small relative to the amount of the terminal arylcarbonate groups. That is, it is preferred that the molar ratio of theterminal groups of the prepolymer, namely the molar ratio of ##STR8## bewithin the range of from 5/95 to 49/51. On the other hand, when it isintended to produce an aromatic polycarbonate having a chemicallyreactive terminal hydroxyl group in a relatively large amount, it ispreferred that the ratio of ##STR9## of the prepolymer be within therange of from 51/49 to 95/5.

The porous, crystallized, aromatic polycarbonate produced by solid-statecondensation polymerization (hereinafter, frequently referred to simplyas "solid-state polymerization") of each of the above-mentionedprepolymers having molar ratios of the terminal groups within theabove-mentioned different ranges, generally has, as terminal groups,both hydroxyl groups and aryl carbonate groups. However, if desired, itis possible that the molar ratio of the terminal groups of theprepolymer is appropriately changed so as to produce an aromaticpolycarbonate having, as terminal groups, hydroxyl groups only or arylcarbonate groups only.

Further, the prepolymer may also contain other terminal groups, forexample ethyl carbonate groups, in addition to the terminal hydroxyl andaryl carbonate groups, as described later. In such a case, theabove-mentioned ratio of the terminal groups is represented by the molarratio of the total of the hydroxyl groups and other terminal groups(e.g., ethyl carbonate groups) to the aryl carbonate groups.

Aromatic group Ar of the recurring aromatic carbonate units ispreferably a divalent aromatic group represented by, for example,formula (VI):

    --Ar.sup.1 --Y--Ar.sup.2 --                                (VI),

wherein each of Ar¹ and Ar² independently represents a divalentcarbocyclic or heterocyclic aromatic group having 5 to 30 carbon atoms,and Y represents a divalent alkane group having from 1 to 30 carbonatoms.

Each of divalent aromatic groups Ar¹ and Ar² is either unsubstituted orsubstituted with at least one substituent which does not adverselyaffect the solid-state polymerization reaction. Examples of suitablesubstituents include a halogen atom, an alkyl group having from 1 to 10carbon atoms, an alkoxy group having from 1 to 10 carbon atoms, a phenylgroup, a phenoxy group, a vinyl group, a cyano group, an ester group, anamide group and a nitro group.

As the heterocyclic aromatic group, as used throughout this disclosure,aromatic groups having one or more ring nitrogen atoms, oxygen atoms orsulfur atoms may be mentioned.

Representative examples of divalent aromatic groups include a phenylenegroup, a naphthylene group, a biphenylene group and a pyridylene group,each of which is unsubstituted or substituted with at least onesubstituent, as mentioned above.

Representative examples of divalent alkane groups include organic groupsrepresented by the formulae: ##STR10## wherein each of R¹, R², R³ and R⁴independently represents a hydrogen atom, an alkyl group having from 1to 10 carbon atoms, an alkoxy group having from 1 to 10 carbon atoms, acycloalkyl group having from 5 to 10 ring carbon atoms, a carbocyclicaromatic group having from 5 to 10 ring carbon atoms or a carbocyclicaralkyl group having from 6 to 10 carbon atoms, and k represents aninteger of from 3 to 11, inclusive.

Preferred examples of divalent aromatic groups include those of theformulae: ##STR11## wherein each of R⁵ and R⁶ independently represents ahydrogen atom, a halogen atom an alkyl group having from 1 to 10 carbonatoms, an alkoxy group having from 1 to 10 carbon atoms, a cycloalkylgroup having from 5 to 10 ring carbon atoms or a phenyl group; each of mand n independently represents an integer of from 1 to 4; when m is aninteger of from 2 to 4, each R⁵ may be the same or different; and when nis an integer of from 2 to 4, each R⁶ may be the same or different.

Divalent aromatic group Ar may contain a divalent aromatic grouprepresented by formula (VII):

    --Ar.sup.1 --Z--Ar.sup.2 --                                (VII)

wherein Ar¹ and Ar² are as defined above and Z represents a bond, or adivalent group, such as --O--, --CO--, --S--, --SO--, --SO₂ --, --COO--,and --CON(R¹)--, wherein R¹ is as defined above, in an amount of 0 to 15mole %, based on the total number of moles of all of Ar's.

Examples of such divalent aromatic groups include those of the formulae:##STR12## wherein R⁵, R⁶, m and n have the same meanings as definedabove.

The prepolymer of the present invention may contain, as Ar, one type ofa divalent aromatic group mentioned above. Alternatively, the prepolymermay contain two or more different types of divalent aromatic groups.

The most preferred is a prepolymer containing an unsubstituted orsubstituted bisphenol A group represented by formula (VIII): ##STR13##in an amount of 85 to 100 mole %, based on the total number of moles ofall of Ar's.

The prepolymer may also contain a trivalent aromatic group in an amountof about 0.01 to 3 mole %, based on the total number of moles of all ofAr's.

Ar³ of the terminal aryl carbonate group is either unsubstituted orsubstituted with at least one substituent which does not adverselyaffect the reaction. Examples of suitable substituents include a halogenatom, an alkyl group having from 1 to 10 carbon atoms, an alkoxy grouphaving from 1 to 10 carbon atoms, a phenyl group, a phenoxy group, avinyl group, a cyano group, an ester group, an amide group and a nitrogroup.

Representative examples of monovalent aromatic groups Ar³ include aphenyl group, a naphthyl group, a biphenyl group and a pyridyl group,each of which is unsubstituted or substituted with at least onesubstituent, as mentioned above.

Representative examples of Ar³ include ##STR14##

The porous, crystallized, aromatic polycarbonate prepolymer of thepresent invention has a number average molecular weight of from 1,000 to15,000. When the number average molecular weight is less than 1,000,solid-state polymerization of the prepolymer disadvantageously takes along period of time. Further, the prepolymer is disadvantageouslyfusion-bonded during the solid-state polymerization. On the other hand,it is unnecessary for the prepolymer to have a number average molecularweight of larger than 15,000, because the increase in number averagemolecular weight of the prepolymer larger than 15,000 does not have anyspecial effect on the rate of the solid-state polymerization of theprepolymer. More preferred number average molecular weight is 1,500 to13,000. The most preferred is a number average molecular weight of 2,000to 8,000.

The porous, crystallized, aromatic polycarbonate prepolymer of thepresent invention has a specific surface area of at least 0.2 m² /g.Such a large specific surface area is important for producing an porous,crystallized, aromatic polycarbonate. When the specific surface area issmaller than 0.2 m² /g, the rate of the solid-state polymerization ofthe porous, crystallized, prepolymer is lowered, which isdisadvantageous for producing an aromatic polycarbonate on a commercialscale. The larger the specific surface area of the porous, crystallized,aromatic polycarbonate prepolymer of the present invention, the higherthe rate of the solid-state polymerization becomes, which isadvantageous. From this standpoint, the specific surface area of theporous, crystallized, aromatic polycarbonate prepolymer of the presentinvention is at least 0.2 m² /g , preferably at least 0.5 m² /g, morepreferably at least 0.8 m² /g.

The specific surface area is measured by the Brunauer-Emmett-Tellermethod (BET method) using a krypton gas.

The desired specific surface area of the crystallized prepolymer of thepresent invention, which is as large as 0.2 m² /g or more, is attainedby solvent treatment for crystallizing and simultaneously renderingporous a prepolymer. The scanning electron micrographs of FIGS. 1, 2, 4,5, 6, 7 and 8 clearly show that the prepolymer of the present inventionis porous. For comparison, a scanning electron micrograph of anamorphous prepolymer which has not been subjected to solvent treatmentis shown in FIG. 3, which shows that the amorphous prepolymer isnon-porous.

The porous, aromatic polycarbonate prepolymer of the present inventionis crystalline. The crystallinity of the prepolymer is at least 5% asmeasured by X-ray diffractometry. When the crystallinity of theprepolymer is less than 5%, it is disadvantageous in that the prepolymeris likely to be melted in the course of the solid-state polymerizationfor producing a final polycarbonate, causing the solid-statepolymerization to be difficult to conduct. The upper limit of thecrystallinity is not specifically restricted. However, for subjectingthe prepolymer to solid-state polymerization to produce an aromaticpolycarbonate, it is preferred that the crystallinity be not greaterthan 55% from the standpoint of the rate of solid-state polymerization.For facilitating the solid-state polymerization, the crystallinity ofthe prepolymer is preferably 10 to 45%, more preferably 15 to 40%.

In the present invention, the crystallinity of the porous, crystallizedprepolymer is determined by using the powder X-ray diffraction patternsof a completely amorphous prepolymer and a porous, crystallizedprepolymer (for example, see FIG. 10 and FIG. 11).

Generally, when a crystalline polymer is irradiated with an X-ray,scattered X-rays are observed. The total intensity of the scatteredX-rays is a sum of the X-ray intensity of the crystalline scatteringascribed to the crystalline portion and that of the amorphous scatteringascribed to the amorphous portion. When the weight of the crystallineportion and that of the amorphous portion are expressed as M_(c) andM_(a), respectively, and when the X-ray intensity of the crystallinescattering corresponding to the weight of the crystalline portion andthat of the amorphous scattering corresponding to the weight of theamorphous portion are expressed as I_(c) and I_(a), respectively, andI_(c) and I_(a) are assumed to be able to be distinguished from eachother, the crystallinity X_(c) (%) is calculated from the followingequations: ##EQU1## wherein I_(100c) represents the X-ray intensity of acrystalline scattering per unit weight of the perfectly crystallineportion and I_(100a) represents the X-ray intensity of an amorphousscattering per unit weight of the perfectly amorphous portion.

However, in the present invention, assuming that K=1 with respect to allthe porous, crystallized prepolymers, the crystallinity Xc (%) wascalculated from the following equation: ##EQU2##

The total X-ray diffraction intensity of a sample obtained by X-raydiffractometry is obtained as a sum of the crystalline scatteringintensity, the amorphous scattering intensity and the backgroundintensity due to the scattering by air, the scattering ascribed to thethermal motion of atoms, the Compton scattering and the like. Therefore,for obtaining the crystallinity of the sample, it is necessary toseparate the total X-ray diffraction intensity into the componentintensities mentioned above.

In the present invention, the total X-ray diffraction intensity isseparated into the component intensities as follows. An explanation isgiven referring to FIGS. 10 and 11.

On the powder X-ray diffraction pattern of a porous, crystallizedprepolymer (shown in FIG. 11), straight line P-Q (base line) is drawnbetween the point (P) of 10° (2θ) and the point (Q) of 35° (2θ). Thepoint corresponding to 15° (2θ) on the diffraction intensity curve andthe point corresponding to 15° (2θ) on the base line, at each of whichpoints the crystalline scattering intensity is considered to be zero,are designated R and S, respectively.

On the other hand, on the powder X-ray diffraction pattern of acompletely amorphous prepolymer (shown in FIG. 10) (obtained by meltingthe prepolymer at a temperature of from 280° to 300° C., shaping themolten prepolymer into a sheet form having a thickness of about 1 mm,and rapidly cooling the sheet to 0° C.), straight line K-L (base line)is drawn. Further, the point corresponding to 15° (2θ) on thediffraction intensity curve and the point corresponding to 15° (2θ) onthe base line are designated M and N, respectively.

The following identities are given:

I₁ =the diffraction intensity at point M

B₁ =the diffraction intensity at point N

I₂ =the diffraction intensity at point R

B₂ =the diffraction intensity at point S

Y=the area of the portion surrounded by diffraction intensity curveK-M-L and straight line K-L, and

Z=the area of the portion surrounded by diffraction intensity curveP-R-Q and straight line P-Q.

The crystallinity Xc (%) is calculated from the following equation:##EQU3##

The porous, crystallized, aromatic polycarbonate prepolymer of thepresent invention is, generally, in powder form or in agglomeratedpowder form. The powder form of porous, crystallized, aromaticpolycarbonate prepolymer has an average particle diameter of not greaterthan 250 μm. The agglomerated powder form of porous, crystallized,aromatic polycarbonate prepolymer has an average diameter of not greaterthan 3 mm. In this connection, it should be noted that when a powder oragglomerated powder form of a porous, crystallized, aromaticpolycarbonate prepolymer is subjected to solid-state polymerization, itis preferred that the content of too fine particles in the prepolymer beas small as possible from the standpoint of ease in handling. Further,when the amount of fine particles present in the powder form oragglomerated powder form of the prepolymer is large, it isdisadvantageous in that the particles of both the prepolymer and theformed polymer are likely to be fused and bonded with one another oradhered to a reaction vessel in the course of the solid-statepolymerization. From these standpoints, it is preferred that the contentof particles having a particle diameter as small as 50 μm or less in theprepolymer be not greater than 10% by weight.

According to the present invention, from the viewpoint of ease inhandling, it is preferred that the porous, crystallized, aromaticpolycarbonate prepolymer be in granular form. It is more preferred thatthe granular form of porous, crystallized, aromatic polycarbonateprepolymer have a compressive break strength of at least 5 kgf cm². Whenthe compressive break strength is lower than 5 kgf/cm², it isdisadvantageous in that too fine particles are formed before and duringthe solid-state polymerization, causing the handling of prepolymer to bedifficult. It is preferred that the compressive break strength be aslarge as possible. However, in general, it is sufficient for thegranular form of prepolymer to have a compressive break strength of atleast 5 kgf/cm².

It is most preferred that the above-mentioned granular form ofprepolymer have a crystallinity of at least 5%, preferably not greaterthan 55% (X-ray diffractometry). These granular form of the porous,crystallized prepolymer is advantageous not only in that the handling ofthe prepolymer before and after the solid-state polymerization is easy;the scattering of a powdery prepolymer is avoided when the prepolymer issubjected to solid-state polymerization; and the prepolymer is not fusedduring the solid-state polymerization, but also in that the rate of thesolid-state polymerization can be markedly increased.

The shape of the granular form of prepolymer is not specificallyrestricted, and it may generally be a pellet, sphere, cylinder, disc,polygonal pillar, cube, rectangular parallelepiped, lens or the like.

The average diameter of granules of the granular form of prepolymer maygenerally be 0.5 to 30 mm, preferably 0.8 to 10 mm, more preferably 1 to5 mm. When the average particle diameter is smaller than 0.5 mm, it isdisadvantageous in that the fine particles of the prepolymer scattersand the prepolymer is likely to be fused. On the other hand, thegranular form of prepolymer having an average diameter of greater than30 mm is not preferred from the standpoint of ease in handling.

In the present invention, the diameter of granules of the granular formof prepolymer is defined as the volume average diameter defined in"Zoryu-Binran (Granulation Handbook)", edited by the Society of PowderIndustry in Japan, published in 1975, pp. 19-20. Illustratively stated,the volume average diameter is defined by the following formula:

    Volume average diameter=3Lwh/(Lw+wh+hL),

wherein w is the short axis diameter (which is defined as the distancebetween a pair of parallel lines which is the smallest among thedistances between any pair of parallel lines drawn so as to holdtherebetween the projected image of a granule on a plane, which granuleis stably put on the plane), L is the long axis diameter [which isdefined as the distance between a pair or parallel lines (which areperpendicular to the pair of parallel lines used for defining the shortaxis diameter) drawn so as to hold therebetween the projected image ofthe granule], and h is the height of the granular form of prepolymer.

In another aspect of the present invention, there is provided a methodfor producing a powder form of porous, crystallized, aromaticpolycarbonate prepolymer, which comprises treating an amorphous aromaticpolycarbonate prepolymer with solvent under sufficient shearing force tocrystallize and render porous the amorphous aromatic polycarbonateprepolymer,

the amorphous aromatic polycarbonate prepolymer comprising recurringcarbonate units and terminal hydroxyl and aryl carbonate groups, whereinthe molar ratio of the terminal hydroxyl groups to the terminal arylcarbonate groups is from 5/95 to 95/5, and having a number averagemolecular weight of 1,000 to 15,000,

the shearing force being sufficient to cause the resultant powdery,porous, crystallized, aromatic polycarbonate prepolymer to have anaverage particle diameter of 250 μm or less.

The amorphous aromatic carbonate prepolymer comprising recurringcarbonate groups and having terminal hydroxyl and aryl carbonate groups,and having a number average molecular weight of 1,000 to 15,000, whichis used as a starting material, may generally be prepared bypre-polymerization as will be described later. Then, the amorphousprepolymer is treated with solvent under a high shearing forcesufficient to reduce the prepolymer to particles having an averageparticle diameter of 250 μm or less, to thereby crystallize andsimultaneously render porous the amorphous prepolymer. In this method,the amorphous prepolymer to be treated with solvent may be either in thesolid state or in the molten state. The crystallization and poreformation of the amorphous prepolymer occur from its surface. Therefore,for obtaining a porous, crystallized prepolymer of the present inventionhaving a specific surface area of at least 0.2 m² /g, it is necessarythat the treatment of the prepolymer with solvent be conducted whilemechanically pulverizing the prepolymer under high shearing force to theprepolymer so as to reduce the prepolymer to particles having an averageparticle diameter of 250 μm or less. The average particle diameter usedherein means that of the prepolymer in the solvent which is determinedby a method as will be described later. The mechanical pulverizationunder high shearing force may easily be conducted by a method using anapparatus equipped with a high speed-rotating blade, such as a warningblender, or using a centrifugal pump equipped with a cutter. Forshortening the time required for the crystallization and pore formation,it is preferred that the amorphous prepolymer to be treated with solventbe in the form of a fiber, a strand, a film, beads or the like,irrespective of the state of the amorphous prepolymer, that is, thesolid state or the molten state.

The time required for crystallizing and rendering porous an amorphousprepolymer in solvent is varied according to the type, molecular weightand shape of the amorphous prepolymer, the type of the solvent, thetreating temperature and the like. Generally, the crystallization andpore formation may be accomplished within several seconds to severalhours. The temperature may generally be chosen in the range of from -10°to 200° C. From the standpoints of the crystallization rate and ease inobtaining a porous, crystallized, aromatic polycarbonate prepolymerhaving a large specific surface area, it is preferred that thecrystallization be conducted at a temperature as high as possible withinthe above-mentioned range.

Representative examples of solvents which can be used for crystallizingand rendering porous the amorphous prepolymer include halogenatedaliphatic hydrocarbons, such as methyl chloride, methylene chloride,chloroform, tetrachloromethane, ethyl chloride, dichloroethanes (allposition isomers), trichloroethanes (all position isomers),trichloroethylene and tetrachloroethanes (all position isomers);halogenated aromatic hydrocarbons, such as chlorobenzene anddichlorobenzene; ethers, such as tetrahydrofuran and dioxane; ketones,such as acetone and methylethylketone; aromatic hydrocarbons, such asbenzene, toluene and xylene; and the like. These solvents may be usedindividually or in combination. Of these, acetone is most preferredbecause it is effective for obtaining a porous, crystallized, aromaticpolycarbonate prepolymer having a relatively large specific surfacearea.

The amount of the solvent to be used for crystallizing and renderingporous the amorphous prepolymer is varied according to the types of theamorphous prepolymer and solvent, the desired crystallinity and desiredspecific surface area of the ultimate prepolymer, the crystallizingtemperature, and the like. Generally, the solvent may be used in anamount of 0.1 to 100 times, preferably 0.3 to 50 times the weight of theamorphous prepolymer.

By the above-mentioned method, a powder form of porous, crystallized,aromatic polycarbonate prepolymer having the desired crystallinity andthe desired specific surface area is obtained. Sometimes, the thusobtained powder form of prepolymer contains too fine particles. Forreducing the amount of too fine particles, it is preferred thatparticles (primary particles) of the powder form of prepolymer besubjected to agglomeration to form secondary particles. Thus, theporous, crystallized, aromatic polycarbonate prepolymer is obtained inagglomerated powder form (secondary particle form).

Accordingly, in a further aspect of the present invention, there isprovided a method for producing an agglomerated powder form of porous,crystallized, aromatic polycarbonate prepolymer, which comprisesapplying sufficient pressure or heat to particles of a powder form ofporous, crystallized, aromatic polycarbonate prepolymer mentioned above,to cause the particles to be cohered.

The application of sufficient pressure to particles of a powder form ofporous, crystallized, aromatic polycarbonate prepolymer mayadvantageously be conducted simultaneously with the removal of thesolvent used for crystallizing and rendering porous the amorphousprepolymer after completion of the crystallization and pore formation.Illustratively stated, the solvent is generally removed bycentrifugation, filtration under pressure, filtration under reducedpressure, or the like, by which a pressure is applied to the prepolymersimultaneously. This pressure is sufficient for the agglomeration of apowder, i.e., secondary particle formation. Therefore, agglomeration ofa powder of prepolymer can advantageously be performed simultaneouslywith the removal of the solvent. The thus formed secondary particle(agglomerated powder form) of the prepolymer is stable, and hardly to bereduced to too minute particles even after the solvent is completelyremoved from the prepolymer. The reason for this has not yet beenelucidated, but it is believed that a low molecular weight polycarbonateoligomer present in the prepolymer acts as an adhesive for bonding toominute particles. In view of the above, when the amorphous prepolymercontains a low molecular polycarbonate oligomer in an extremely smallamount, it is preferred that a low molecular weight polycarbonateoligomer be added to the amorphous prepolymer before the crystallizationand pore formation be conducted.

Agglomeration for forming secondary particles may also be conductedutilizing the fusion-bonding property of the powder form of prepolymer.That is, a powder form of prepolymer is sufficiently heated to such atemperature that the surfaces of the particles of the prepolymer arefused slightly, to thereby agglomerate the powder.

In the above-mentioned method, a powder form of porous, crystallized,aromatic polycarbonate prepolymer to be used as a starting material forproducing an agglomerated form of prepolymer has a specific surface areaof at least 0.2 m² /g, preferably at least 0.5 m² /g. The crystallinityof the powder form of prepolymer is at least 5%, preferably not greaterthan 55%.

The thus obtained powder or agglomerated powder form of porous,crystallized, aromatic polycarbonate prepolymer may be granulated toproduce a granular form of porous, crystallized, aromatic polycarbonateprepolymer mentioned above. Thus, in still a further aspect of thepresent invention, there is provided a method for producing a granularform of porous, crystallized, aromatic polycarbonate prepolymer, whichcomprises granulating a powder form or an agglomerated powder form ofporous, crystallized, aromatic polycarbonate prepolymer.

The method for granulating the powder or agglomerated powder form ofprepolymer is not specifically restricted. Generally, granulation of theprepolymer can easily be performed by a conventional method, such as arolling method, a vibration method, a compression molding method and anextrusion molding method. Of these methods, extrusion-granulation by anextrusion molding method and compression-granulation by a compressionmolding method are most preferred, because a granular shaped article ofthe present invention having a compressive break strength of at least 5kgf cm² can easily be produced. The granulation can advantageously beperformed, using a commercially available tablet machine or granulator,at a temperature of not greater than the crystalline melting point ofthe prepolymer, preferably 0° to 100° C.

Production of a granular form of prepolymer may be conducted in drystate using a dry powder form or a dry agglomerated powder form ofporous, crystallized prepolymer, or in wet state using a powder form oran agglomerated powder form of prepolymer wetted with an appropriateliquid. Preferred is the wet state method, because a powder form or anagglomerated powder form of prepolymer produced by the crystallizationand pore formation can be subjected to granulation without completelyremoving the solvent therefrom.

The above-mentioned porous, crystallized, aromatic polycarbonateprepolymers in powder form, agglomerated powder form and granular formcan advantageously be used as prepolymers to be subjected to solid-statecondensation polymerization, to thereby produce porous, crystallized,aromatic polycarbonates. From the powder form or an agglomerate powderform of prepolymer, a powder form or an agglomerated powder form ofporous, crystallized, aromatic polycarbonate is produced. On the otherhand, from the granular form of prepolymer, a granular form of porous,crystallized, aromatic polycarbonate is produced.

Hereinbelow, an explanation is given with respect to the production of apowder form or an agglomerated powder form of porous, crystallized,aromatic polycarbonate. That is, according to the present invention,there is provided a method for producing a powder form or anagglomerated powder form of porous, crystallized, aromatic polycarbonatehaving a number average molecular weight of from 6,000 to 200,000 and acrystallinity of at least 35%, which comprises heating a powder form oran agglomerated powder form of porous, crystallized, aromaticpolycarbonate prepolymer in a heating zone, at a temperature which ishigher than the glass transition temperature of the prepolymer and atwhich the prepolymer is in a solid state, to effect solid-statecondensation polymerization of the prepolymer while removingcondensation polymerization by-products from the heating zone,

thereby increasing the number average molecular weight and thecrystallinity of the prepolymer to from 6,000 to 200,000 and at least35%, respectively, so that the resultant polycarbonate has a numberaverage molecular weight and a crystallinity which are, respectively,greater than those of the prepolymer.

In the above method, it is more preferred that the porous, crystallized,aromatic carbonate prepolymer to be subjected to solid-statepolymerization have a specific surface area of at least 0.5 m² /g.Further, it is preferred that the porous, crystallized aromaticcarbonate prepolymer have a crystallinity of from 5 to 55%.

The solid-state polymerization in the method of the present invention isconducted by heating a powder form or an agglomerated powder form ofporous, crystallized, aromatic polycarbonate prepolymer in a heatingzone. The temperature (Tp, °C.) and time required for the solid-statepolymerization vary depending upon the chemical structure, molecularweight, crystallinity, melting point (Tm, ° C.) and shape of the porous,crystallized, aromatic polycarbonate prepolymer; the presence or absenceof a catalyst remaining in the porous, crystallized, aromaticpolycarbonate prepolymer; the type and amount of a catalyst, if any, inthe porous, crystallized, aromatic polycarbonate prepolymer; the typeand amount of a catalyst if added to the polymerization system; thespecific surface area of the porous, crystallized, aromaticpolycarbonate prepolymer; the polymerization degree of the desiredcrystallized, aromatic polycarbonate; and the like. But, the solid-statepolymerization must be conducted at a temperature which is higher thanthe glass transition temperature of the porous, crystallized prepolymerand at which the porous, crystallized, aromatic polycarbonate prepolymeris not melted but in a solid state (namely, a temperature of lower thanthe crystalline melting temperature of the prepolymer). It is morepreferred that the solid-state polymerization be conducted at atemperature (Tp, °C.) satisfying the following relationships:

    Tm-50≦Tp<Tm                                         (v)

wherein Tp and Tm are as defined above. In this connection, it is to benoted that both the glass transition temperature and the crystallinemelting temperature of the prepolymer are elevated with the progress ofthe polymerization of the prepolymer. Therefore, the suitabletemperature for solid-state polymerization also becomes high with theprogress of the polymerization. The reaction time for solid-statepolymerization is generally in the range of from one minute to 100hours, preferably in the range of from 0.1 to 50 hours. With respect tothe temperature for solid-state polymerization, for example, when apolycarbonate is prepared from bisphenol A, the temperature for thesolid-state polymerization is in the range of from about 150° to about260° C., preferably from about 180° to about 230° C.

In the solid-state condensation polymerization, condensationpolymerization by-products, such as an aromatic monohydroxyl compoundand a diaryl carbonate, are formed in the heating zone. The solid-statecondensation polymerization reaction may be accelerated by removing theby-products from the polymerization reaction system. The by-products maybe removed by a method in which the polymerization reaction is carriedout under reduced pressure, or a method in which an inert gas is flowedinto the heating zone and the inert gas containing the condensationpolymerization by-products is discharged from the heating zone. The term"inert gas" used herein means not only those defined by the so-calledinert gas as an established term, such as nitrogen gas, argon gas,helium gas and carbon dioxide gas, but also a gas which is not reactiveduring the solid-state polymerization, such as lower hydrocarbon gas andacetone gas. These methods are optionally conducted in combination. Inthe method using an inert gas, it is preferred to heat the gaspreliminarily to a temperature adjacent the polymerization reactiontemperature. The flow rate of the inert gas flowing into the heatingzone may generally be from 0.1 to 10 liters(N.T.P.)/hour, preferablyfrom 0.2 to 7 liters(N.T.P.)/hour, per gram of the porous, crystallized,aromatic polycarbonate prepolymer. The flow rate of the inert gas perunit weight of the prepolymer is important. When the flow rate of theinert gas is less than 0.1 liter(N.T.P.)/hour per gram of theprepolymer, it is disadvantageous in that the rate of the solid-statepolymerization becomes low. On the other hand, when the flow rate of theinert gas is greater than 10 liters(N.T.P.)/hour per gram of theprepolymer, although the rate of the solid-state polymerization becomeshigh, the powder form or agglomerated powder form of porous,crystallized, aromatic carbonate prepolymer is, disadvantageously,likely to scatter in the reaction vessel during the solid-statecondensation polymerization, leading to a fusion-adhesion of theprepolymer to the wall of the reaction vessel and an escape of theprepolymer out of the reaction vessel.

When the solid-state polymerization is conducted while flowing an inertgas into the heating zone, the discharged inert gas may be discardedwithout the re-use thereof. Alternatively, in order to reduce theproduction cost, the discharged inert gas may be recovered and re-used.The discharged inert gas contains condensation polymerizationby-products mentioned above, such as an aromatic monohydroxyl compoundand a diaryl carbonate. Therefore, it has been considered that when thedischarged inert gas is recovered and re-used, it is necessary to removethe by-products contained in the inert gas. However, it has unexpectedlybeen found that even if the inert gas contains the by-products, when thecontent of the condensation polymerization by-products of the dischargedinert gas is 5 mmHg or less in terms of the partial pressure of theby-products in the inert gas, such an inert gas containing theby-products can be re-used for the solid-state condensationpolymerization of the prepolymer, and the condensation polymerizationcan advantageously be performed. Therefore, in the method of the presentinvention, the discharged inert gas having a by-products content of 5mmHg or less in terms of the partial pressure of the by-products in theinert gas may advantageously be flowed into the heating zone as theinert gas and re-used for the solid-state polymerization. Of course,from the standpoint of complete avoidance of the adverse reaction duringthe solid-state polymerization, it is most preferred that theby-products be completely removed from the discharged inert gas.However, it is extremely difficult to remove the by-products from thedischarged inert gas to an extent that the content of the by-products inthe discharged inert gas is less than 0.01 mmHg in terms of the partialpressure. The reduction of the by-products content in the inert gas maygenerally be conducted by removing the by-products from the dischargedinert gas or by diluting the discharged inert gas with a fresh inertgas.

The solid-state polymerization according to the method of the presentinvention may be carried out by using a batch-wise method or acontinuous method, or by using both methods in combination. As a reactorfor the solid-state condensation polymerization, various types ofreactors, for example, a tumbler type, a kiln type, a paddle-dryer type,a screw-conveyer type, a vibrator type, a fluidized-bed type, afixed-bed type, a moving bed type and the like can be used.

The solid-state condensation polymerization for producing the porous,crystallized, aromatic polycarbonate from the porous, crystallizedprepolymer may be performed at an economically satisfactory reactionrate without using a catalyst. This is the most preferred mode of thepresent method. Alternatively, a catalyst may be added in order toaccelerate the polymerization reaction rate. However, when a catalyst isused, such a catalyst is likely to remain in the final aromaticpolycarbonate as an impurity and such a impurity catalyst often hasadverse effects on the physical properties of the aromatic polycarbonate(such as color, heat resistance, boiled water resistance andweatherability). Therefore, it is preferred that the amount of acatalyst to be used be as small as possible.

When the porous, crystallized, aromatic polycarbonate prepolymer of thepresent invention to be used as a starting material for producing aporous, crystallized, aromatic polycarbonate is produced using acatalyst, the catalyst generally remains in the prepolymer and,therefore, a further catalyst need not be added to the solid-statepolymerization system. However, in the case where the catalyst isremoved or inactivated in the course of the crystallization and poreformation of the prepolymer and it is still desired to accelerate thesolid-state polymerization, an appropriate catalyst may optionally beadded to the solid-state polymerization reaction system. In this case, acatalyst may be added in a liquid or gas form to a polymerization systemof the porous, crystallized prepolymer. As such a catalyst, anycondensation polymerization catalyst conventionarily used in the art canbe used. Examples of such catalysts include hydroxides of an alkali oralkaline earth metal, such as lithium hydroxide, sodium hydroxide,potassium hydroxide and calcium hydroxide; hydrides of an alkali oralkaline earth metal, such as lithium hydride, sodium hydride andcalcium hydride; alkali metal salts, alkaline earth metal salts andquarternary ammonium salts of boron hydride or aluminum hydride, such aslithium aluminum hydride, sodium boron hydride and tetramethyl ammoniumboron hydride; alkoxides of an alkali or alkaline earth metal, such aslithium methoxide, sodium ethoxide and calcium methoxide; aryloxides ofan alkali or alkaline earth metal, such as lithium phenoxide, sodiumphenoxide, magnesium phenoxide, LiO-Ar-OLi wherein Ar is an aryl groupand NaO-Ar-ONa wherein Ar is as defined above; organic acid salts of analkali or alkaline earth metal, such as lithium acetate, calcium acetateand sodium benzoate; zinc compounds, such as zinc oxide, zinc acetateand zinc phenoxide; boron compounds, such as boron oxide, boric acid,sodium borate, trimethyl borate, tributyl borate and triphenyl borate;silicon compounds, such as silicon oxide, sodium silicate,tetraalkylsilicon, tetraarylsilicon and diphenyl-ethyl-ethoxysilicon;germanium compounds, such as germanium oxide, germanium tetrachloride,germanium ethoxide and germanium phenoxide; tin compounds, such as tinoxide, dialkyltin oxide, diaryltin oxide, dialkyltin carboxylate, tinacetate, tin compounds having an alkoxy group or aryloxy group bonded totin, such as ethyltin tributoxide and organotin compounds; leadcompounds, such as lead oxide, lead acetate, lead carbonate, basic leadcarbonate, and alkoxides and aryloxides of lead or organolead; oniumcompounds, such as a quaternary ammonium salt, a quaternary phosphoniumsalt and a quaternary arsonium salt; antimony compounds, such asantimony oxide and antimony acetate; manganese compounds, such asmanganese acetate, manganese carbonate and manganese borate; titaniumcompounds, such as titanium oxide and titanium alkoxides and titaniumaryloxides; and zirconium compounds, such as zirconium acetate,zirconium oxide, zirconium alkoxides and zirconium aryloxides andzirconium acetylacetone.

These catalysts may be used individually or in combination. The amountof catalyst to be used is as follows. When a catalyst containing a metalis used, the amount of the catalyst is generally in the range of from 1ppm to 500 ppm by weight, in terms of the amount of the metal containedin the catalyst, based on the weight of the porous, crystallized,aromatic polycarbonate prepolymer used as the starting material. When acatalyst containing no metal is used, the amount of the catalyst isgenerally in the range of from 1 ppm to 500 ppm by weight, in terms ofthe amount of the atom as a cation species contained in the catalyst,based on the weight of the prepolymer.

As mentioned above, in the method of the present invention, the intendedprepolymer can readily be prepared in the absence of any catalyst, andthe aromatic polycarbonate produced without using a catalyst has anextremely excellent properties. This is one of the main features of thepresent invention. In the present invention, the terminology "in theabsence of a catalyst" means that the amount of a catalyst is smallerthan 1 ppm that is the minimum in the above-mentioned amount range.

According to the above-mentioned method of the present invention, apowder form or an agglomerated powder form of porous, crystallized,aromatic polycarbonate having a number average molecular weight of from6,000 to 200,000 and a crystallinity of at least 35%, wherein the numberaverage molecular weight and crystallinity of the aromatic polycarbonateare greater than those of the porous, crystallized prepolymer used as astarting material, can easily be produced.

Further, according to the method of the present invention, a powder formor an agglomerated powder form of porous, crystallized, aromaticpolycarbonate having a specific surface area of at least 0.1 m² /g canadvantageously be produced.

Furthermore, according to the method of the present invention, a powderform or an agglomerated powder form of porous, crystallized, aromaticpolycarbonate having a crystallinity of not greater than 70%, which isgreater than that of the prepolymer used as a starting material, caneasily be obtained.

Next, an explanation is given with respect to the production of agranular form of porous, crystallized, aromatic polycarbonate. That is,according to the present invention, there is provided a method forproducing a granular form of porous, crystallized, aromaticpolycarbonate having a number average molecular weight of from 6,000 to200,000 and a crystallinity of at least 35%, which comprises heating agranular form of porous, crystallized, aromatic polycarbonate prepolymerin a heating zone, at a temperature which is higher than the glasstransition temperature of said prepolymer and at which said prepolymeris in a solid state, to effect solid-state condensation polymerizationof said prepolymer while removing condensation polymerizationby-products from the heating zone,

thereby increasing the number average molecular weight and thecrystallinity of the prepolymer to from 6,000 to 200,000 and at least35%, respectively, so that the resultant polycarbonate has a numberaverage molecular weight and a crystallinity which are, respectively,greater than those of said granular prepolymer.

The heating of granular form of porous, crystallized, aromaticpolycarbonate prepolymer can be conducted in substantially the samemanner as in the production of the powder form or the agglomeratedpowder form of polycarbonate mentioned above, except that a granularform of porous, crystallized, aromatic polycarbonate prepolymer is usedas a starting material. In practicing the above-mentioned method, it ispreferred that the heating of the granular form of prepolymer beconducted while flowing an inert gas into the heating zone and whiledischarging the inert gas containing the condensation polymerizationby-products from the heating zone. The flow rate of the inert gas maygenerally be in the range of from 0.1 to 50 liters(N.T.P.)/hour, pergram of the granular form of prepolymer. In the case of the solid-statepolymerization of the granular form of prepolymer, there is no problemof the scattering of the prepolymer. Therefore, the flow rate of theinert gas can be increased up to 50 liters(N.T.P.)/hour, per gram of thegranular form of prepolymer. The rate of the solid-state polymerizationcan be increased by increasing the flow rate of the inert gas. However,even when the flow rate of the inert gas is increased to higher than 50liters(N.T.P.)/hour, per gram of the granular form of prepolymer, therate of the solid-state polymerization is no longer increased.Therefore, it is not necessary that the flow rate of the inert gas beincreased to higher than 50 liters(N.T.P.)/hour, per gram of thegranular form of prepolymer. From the standpoint of the improvement ofthe polymerization degree, the flow rate of the inert gas is preferablyin the range of from 0.2 to 30 liters (N.T.P.)/hour, per gram of thegranular form of prepolymer.

As in the case of the production of a powder form or an agglomeratedpowder form of polycarbonate, it is preferred that the condensationpolymerization by-products be removed from the discharged inert gas, orthe discharged inert gas be diluted with an inert gas, so that theresultant gas has a condensation polymerization by-products content of 5mmHg or less in terms of the partial pressure of the condensationpolymerization by-products in the inert gas, and the resultant gas beflowed into the heating zone as the inert gas.

The granular form of porous, crystallized, aromatic polycarbonateproduced by the above-mentioned method of the present inventioncomprises terminal hydroxyl groups and/or terminal aryl carbonategroups, and has a number average molecular weight of from 6,000 to200,000 and a crystallinity of from 35 to 70%, which are, respectively,greater than those of the granular form of prepolymer. In thisconnection, it is preferred that the crystal-linity of the granular formof porous, crystallized, aromatic polycarbonate be not greater than 70%.Further, it is also preferred that the specific surface area of thegranular polycarbonate be at least 0.1 m² /g.

The granular form of porous, crystallized, aromatic polycarbonate thusproduced from the granular, prepolymer has a compressive break strengthof at least 10 kgf/cm² which is greater than that of the granular formof prepolymer. This fact is unexpected and surprising. It has beenconsidered that the compressive break strength of the granular form ofpolycarbonate is lower than that of the granular form of prepolymer.That is, it has been considered that the polymerization by-products,such as phenols and diaryl carbonate, are removed during the solid-statecondensation polymerization, and by the removal of the by-productscontained in the prepolymer, voids would be likely to be formed in theproduced polycarbonate, which would result in a decrease in mechanicalstrength of the resultant polycarbonate.

The granular form of porous, crystallized, aromatic polycarbonate hassubstantially the same shape and diameter as those of the granular formof porous, crystallized, aromatic polycarbonate prepolymer which is usedas a starting material. Therefore, the granular polycarbonate,generally, has a shape of a pellet, sheet, disk, cylinder, polygonalpillar, cube, rectangular parallelepiped or sphere, and has a diameterof 0.5 to 30 mm.

The powder form, the agglomerated powder form or the granular form ofporous, crystallized, aromatic polycarbonate comprising recurringaromatic carbonate units and terminal hydroxyl and/or aryl carbonategroups and having a specific surface area of at least 0.1 m² /g, anumber average molecular weight of from 6,000 to 200,000 and acrystallinity of at least 35%, may be subjected to molding at atemperature lower than the glass transition temperature of thepolycarbonate, to thereby obtain a shaped, porous, crystallized,aromatic polycarbonate. The thus obtained shaped polycarbonate has abulk density of from 0.1 to 1.1 g/cm³ and a compressive break strengthof at least 10 kgf/cm². Therefore, according to the present invention,there is provided a method for producing a shaped, porous, crystallizedaromatic polycarbonate having a bulk density of from 0.1 to 1.1 g/cm³and a compressive break strength of at least 10 kgf/cm², which comprisessubjecting a powder form, an agglomerated powder form or a granular formof porous, crystallized aromatic polycarbonate to molding at atemperature which is lower than the glass transition temperature of thepolycarbonate,

the powder form, the agglomerated form or the granular form of porous,crystallized, aromatic polycarbonate comprising recurring aromaticcarbonate units and terminal hydroxyl and/or aryl carbonate groups andhaving a specific surface area of at least 0.1 m^(2/) g, a numberaverage molecular weight of from 6,000 to 200,000 and a crystallinity ofat least 35%.

In the above-mentioned method of the present invention, the molding ofthe porous, crystallized aromatic polycarbonate may generally beconducted by compression molding or by extrusion molding at atemperature lower than glass transition temperature of thepolycarbonate.

The powder form or agglomerated powder form of the porous, crystallized,aromatic polycarbonate of the present invention is not hydrolyzed duringthe molding, even when the polycarbonate is subjected to molding withoutdrying the polycarbonate before molding. This is due to its extremelysmall equilibrium moisture content which is ascribed to its highcrystallinity. Accordingly, the powder form or the agglomerated powderform of porous, crystallized, aromatic polycarbonate also canadvantageously be subjected to conventional molding method, such asrotational molding and sinter molding, to prepare a shaped article.

A shaped polycarbonate can also be produced by heating the porous,crystallized, aromatic polycarbonate of the present invention. That is,according to the present invention, there is provided a method forproducing a shaped, porous, crystallized aromatic polycarbonate having abulk density of from 0.1 to 1.1 g/cm³ and a compressive break strengthof at least 10 kgf/cm², which comprises heating particles of a powderform or of an agglomerated powder form of porous, crystallized aromaticpolycarbonate, or heating granules of a granular form of porous,crystallized aromatic polycarbonate, at a temperature which is higherthan the glass transition temperature of the polycarbonate and which islower than the crystalline melting temperature of the polycarbonate, tofuse and bond the surfaces of the particles or of the granules,

the powder form, the agglomerated powder form or the granular form ofporous, crystallized aromatic polycarbonate comprising recurringaromatic carbonate units and terminal hydroxyl and/or aryl carbonategroups and having a specific surface area of at least 0.1 m² /g, anumber average molecular weight of from 6,000 to 200,000 and acrystallinity of at least 35%. In this method, the heating of theparticles of the powder form or the agglomerated powder form of porous,crystallized aromatic polycarbonate or the heating of the granular formof porous, crystallized aromatic polycarbonate is conducted at atemperature which is higher than the glass transition temperature of thepolycarbonate and which is lower than the crystalline melting point ofthe polycarbonate. Generally, the heating may be conducted at 160° to250° C. under a compressive load at 0.1 to 2 tf cm².

By the above mentioned method, a shaped article having excellentproperties as will be described later can be obtained. Therefore,according to the present invention, there is provided a shaped, porous,crystallized aromatic polycarbonate comprising recurring aromaticcarbonate units and terminal hydroxyl and/or aryl carbonate groups, andhaving a number average molecular weight of from 6,000 to 200,000, abulk density of from 0.1 to 1.1 g/cm³, a crystallinity of at least 35%and a compressive break strength of at least 10 kgf/cm².

In this connection, it is preferred that the shaped article have aspecific surface area of at least 0.1 m² /g. Further, it is alsopreferred that the crystallinity of the shaped polycarbonate be notgreater than 70%.

The shaped, porous, crystallized aromatic polycarbonate may be in anyform, e.g., a shape of a granule, pellet, sheet, disc, cylinder,polygonal pillar, cube, rectangular parallelepiped or sphere.

Each of the powder form or agglomerated powder form of porous,crystallized, aromatic polycarbonate, the granular form of porous,crystallized, aromatic polycarbonate and the shaped, porous,crystallized, aromatic polycarbonate of the present invention has ahigh, sharp crystalline melting point as well as a high crystallinity.These properties clearly distinguish the aromatic polycarbonate of thepresent invention and the shaped article thereof from the aromaticpolycarbonate produced by the conventional phosgene process or meltprocess (transesterification process) mentioned hereinbefore. Such ahigh crystallinity of each of the porous, crystallized aromaticpolycarbonate and the shaped article thereof of the present invention ispresumed to be ascribed to the re-arrangement of the molecular chains ofthe porous, crystallized prepolymer, which is caused during thesolid-state condensation polymerization. The crystalline melting pointof the aromatic polycarbonate of the present invention is determined,using 5 to 10 mg of a polycarbonate sample, by means of a differentialscanning calorimeter (hereinafter referred to as "DSC") in anatomosphere of an inert gas at a heating rate of 10° C./min. Forexample, in the case of the aromatic polycarbonate produced usingbisphenol A, the peak of the crystalline melting point is at 230° to300° C., and the half width of the peak of the crystalline melting pointis 3° to 8° C.

The porous, crystallized, aromatic polycarbonate of the presentinvention and the shaped article produced therefrom, both of which havehigh crystallinity, is excellent in resistance to chemicals and solventas compared to the conventional amorphous aromatic polycarbonate.Therefore, the crystallized aromatic polycarbonate can advantageously beused as a sintering material, filter, absorbent of a gas or a liquid,wall covering material and heat insulating material, and may havevarious shapes, for example, a pellet, sheet, disk, cylinder, polygonalpillar cube, rectangular pallalelepiped or sphere.

Following is a chart showing the relationships between aromaticpolycarbonate prepolymers and polycarbonates produced therefrom.##STR15##

Hereinbelow, an explanation is given with respect to the preparation ofan amorphous, aromatic polycarbonate prepolymer which is used as astarting material for producing a porous, crystallized, aromaticpolycarbonate prepolymer of the present invention. The method forpreparing the amorphous prepolymer is not specifically restricted.Generally, the following methods may be used.

Method (1): a transesterification is performed between an aromaticdihydroxyl compound and a diaryl carbonate.

Method (2): an aromatic dihydroxy compound and a diaryl carbonate arereacted with each other in a molar ratio of from 1:1.2 to 1:2 to preparean aromatic polycarbonate oligomer containing terminal groups comprisedmainly of aryl carbonate groups and having a number average molecularweight of about 350 to 950 and, then, a transesterification is performedbetween the oligomer and an aromatic dihydroxy compound.

Method (3): an aromatic dihydroxy compound and a diaryl carbonate arereacted with each other in a molar ratio of from 1.2:1 to 2:1 to preparean aromatic polycarbonate oligomer containing terminal groups comprisedmainly of hydroxyl groups and having a number average molecular weightof about 350 to 950 and, then, a transesterification is performedbetween the oligomer and a diaryl carbonate.

Method (4): an aromatic dihydroxy compound and phosgene are subjected tointerfacial condensation polymerization in the presence of a molecularweight controller.

Method (5): an aromatic dihydroxy compound is subjected to interfacialcondensation polymerization together with phosgene and an aromaticmonohydroxy compound (molecular weight controller) in excess amountsrelative to the amount of the aromatic dihydroxy compound, to prepare anaromatic carbonate oligomer containing terminal groups comprised mainlyof aryl carbonate groups and having a number average molecular weight ofabout 350 to 950 and, then, a transesterification is performed betweenthe oligomer and an aromatic dihydroxy compound.

By any of Method (1), (2) and (3), an amorphous aromatic polycarbonateprepolymer containing substantially no chlorine compound can easily beproduced advantageously. From such an amorphous aromatic polycarbonateprepolymer, a porous, crystallized, aromatic polycarbonate prepolymerand a porous, crystallized aromatic polycarbonate, each containingsubstantially no chlorine compound, can advantageously be produced.

On the other hand, according to Method (4) or (5) in which phosgene isused, each of the obtained aromatic polycarbonate prepolymer which is afinal product of each of Methods (4) and (5) and the aromaticpolycarbonate oligomer which is an intermediate product, contains achlorine compound. However, when each of the aromatic polycarbonateprepolymer and the oligomer has a relatively low molecular weight, thechlorine compound can easily be removed from each of the prepolymer andthe oligomer. Therefore, even according to Method (4) or (5), anaromatic polycarbonate having a lower molecular weight and containingsubstantially no chlorine compound can easily be obtained.

The aromatic dihydroxy compound and the diaryl compound which may beused as raw materials for preparing an amorphous aromatic polycarbonateprepolymer is represented by formulae (IX) and (X):

    HO--Ar--OH                                                 (IX),

wherein Ar has the same meaning as defined above; and ##STR16## whereinAr³ has the same meaning as defined above.

Representative examples of diaryl carbonates include substituted orunsubstituted diphenyl carbonates represented by the formula: ##STR17##wherein each of R⁷ and R⁸ independently represents a hydrogen atom, ahalogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxygroup having 1 to 10 carbon atoms, a cycloalkyl group having from 5 to10 ring carbon atoms or a phenyl group; and each of p and qindependently represents an integer of from 1 to 5; with the provisothat when p is an integer of from 2 to 5, each R⁷ may be the same ordifferent, and when q is an integer of from 2 to 5, each R⁸ may be thesame or different.

Of these diphenyl carbonates, preferred are diaryl carbonates having asymmetrical configuration, such as diphenyl carbonate, ditolyl carbonateand diphenyl carbonate substituted with a lower alkyl group, e.g.di-t-butylphenyl carbonate. Of these, diphenyl carbonate is mostpreferred because of the simplest structure.

The above-mentioned diaryl carbonates are used individually or incombination. However, when two or more different types of diarylcarbonates are used, the reaction system becomes complicated with littleadvantage. Therefore, it is preferred to use one type of diarylcarbonate having a symmetrical configuration, individually.

As the molecular weight controller to be employed in the interfacialcondensation polymerization method, there may be mentioned the aromaticmonohydroxy compound represented by formula (XI):

    Ar.sup.3 --OH                                              (XI)

wherein Ar³ has the same meaning as defined above.

Preferable examples of aromatic monohydroxy compounds include phenol,o-, m- or p-cresol, 2,6-xylenol, p-t-butylphenol andp-octylphenols(including various position isomers). Of these, phenol andp-t-butylphenol are particularly preferred.

Further, another type of molecular weight controller may alsoadvantageously be used in combination with the above-mentioned aromaticmonohydroxy compound. Examples of molecular weight controllers of thistype include monohydric alcohols, such as methanol and ethanol;haloformates, such as methyl chloroformate, ethyl chloroformate,isopropyl chloroformate and cyclohexyl chloroformate; monovalent thiols,such as methyl mercaptan and ethyl mercaptan; monovalenthalothioformates, such as methyl chlorothioformate and ethylchlorothioformate; monocarboxylic acid such as acetic acid, propionicacid, benzoic acid, sodium acetate, acetic anhydride and acetylchloride, propionyl chloride and derivatives thereof.

In order to facilitate the pre-polymerization, a dibasic acid or areactive derivative thereof may optionally be used in an amount of 5mole % or less based on the number of moles of the aromatic dihydroxycompound. The above dibasic acid and reactive derivatives thereof may bealiphatic, aromatic or alicyclic. Examples of dibasic acids and reactivederivatives thereof include dibasic acids, such as terephthalic acid,isophthalic acid, phthalic acid, naphthalene-1,5-dicarboxylic acid,diphenyl-2,2'-dicarboxylic acid, cis-1,2-cyclohexane dicarboxylic acid,oxalic acid, succinic acid, sebacic acid, adipic acid, maleic acid andfumaric acid; and alkali metal salts, alkaline earth metal salts, aminesalts and halides thereof.

An explanation is given below with respect to preferred modes of themethod of the present invention for producing a porous, crystallizedaromatic polycarbonate. Examples of preferred modes include thefollowing methods (A), (B) and (C).

Method (A) for producing a porous, crystallized, aromatic polycarbonatefrom an aromatic dihydroxy compound and diaryl carbonate comprises thesteps of:

(1) reacting an aromatic dihydroxy compound with an aromatic carbonateunder heating at a temperature sufficient and for a period of timesufficient to prepare an amorphous prepolymer having a number averagemolecular weight of from 1,000 to 15,000 and having terminal hydroxyland aryl carbonate groups (pre-polymerization);

(2) treating the amorphous prepolymer with solvent under sufficientshearing force to crystallize to a crystallinity of at least 5% andsimultaneously render porous the prepolymer, the shearing force beingsufficient to cause the resultant powder form of porous, crystallized,aromatic polycarbonate prepolymer to have an average particle diameterof 250 μm or less, the resultant powder form of porous, crystallizedprepolymer having a specific surface area of at least 0.2 m² /g; and

(3) heating the powder form of porous, crystallized prepolymer, orheating an agglomerated powder form or a granular form of porous,crystallized prepolymer derived from the powder form of prepolymer, at atemperature which is higher than the glass transition temperature of thecrystallized prepolymer and at which the crystallized prepolymer is in asolid state, to effect solid-state condensation polymerization of thecrystallized prepolymer, thereby increasing the number average molecularweight and the crystallinity of the crystallized prepolymer to from6,000 to 200,000 and at least 35%, respectively, so that the resultantpolycarbonate has a number average molecular weight and a crystallinitywhich are, respectively, greater than those of the crystallizedprepolymer.

In method (A), an amorphous prepolymer is prepared in thepre-polymerization step (1) and then crystallized and rendered porous instep (2). Subsequently, the porous, crystallized, prepolymer obtained inStep (2) is subjected to solid-state condensation polymerization in step(3). In prepolymerization step (1), a mixture of an aromatic dihydroxycompound and a diaryl carbonate is heated, while removing a by-producedaromatic monohydroxy compound having a structure such that a hydroxylgroup is bonded to an aryl group derived from the diaryl carbonate, tothereby obtain a prepolymer.

The number average molecular weight of the amorphous prepolymer preparedin pre-polymerization step (1) is generally within the range of from1,000 to 15,000. The number average molecular weight of the amorphousprepolymer can be controlled by appropriately selecting reactionconditions, such as temperature, reaction time, pressure and agitationrate. In general, the pre-polymerization is performed at a temperatureof from 100° to 320° C., preferably of from 160° to 280° C., for aperiod of from 0.5 to 20 hours under atmospheric pressure or reducedpressure.

The pre-polymerization is preferably effected in molten state withoutusing a solvent. Alternatively, the pre-polymerization may be performedin a solvent which is inert to the pre-polymerization reaction, such asmethylene chloride, chloroform, 1,2-dichloroethane, tetrachloroethane,dichlorobenzene, tetrahydrofuran, diphenylmethane and diphenyl ether.

The molar ratio of the diaryl carbonate to the aromatic dihydroxycompound is varied depending on the types of the employed diarylcarbonate and aromatic dihydroxy compound, the reaction conditions, suchas reaction temperature. The diaryl carbonate may be used in an amountof from 0.6 to 1.8 moles, preferably from 0.7 to 1.6 moles, morepreferably from 0.8 to 1.5 moles, per mole of the aromatic dihydroxycompound.

The amorphous prepolymer prepared in the abovementionedpre-polymerization generally comprises terminal aryl carbonate groupsrepresented, for example, by the formula: ##STR18## wherein Ar³ has thesame meaning as defined above, and terminal hydroxyl groups derived fromthe dihydroxydiaryl compound, which is represented, for example, by theformula:

    HO--Ar--

wherein Ar has the same meaning as defined above.

The crystallization and pore formation in step (2) and the solid-statecondensation polymerization in step (3) are conducted in the same manneras described hereinbefore in detail.

Method (B) for producing a crystallized aromatic polycarbonate from anaromatic dihydroxy compound and phosgene comprises the steps of:

(1) reacting an aromatic dihydroxy compound with phosgene in thepresence of a molecular weight controller to prepare a prepolymer havinga number average molecular weight of from 1,000 to 15,000(pre-polymerization);

(2) treating said prepolymer with solvent under sufficient shearingforce to crystallize to a crystallinity of at least 5% andsimultaneously render porous said prepolymer, the shearing force beingsufficient to cause the resultant powder form of porous, crystallized,aromatic polycarbonate prepolymer to have an average particle diameterof 250 μm or less, the resultant powder form of porous, crystallizedprepolymer having a specific surface area being at least 0.2 m² /g; and

(3) heating the powder form of porous, crystallized prepolymer, orheating an agglomerated powder form or a granular form of porous,crystallized prepolymer derived from the powder form of prepolymer, at atemperature which is higher than the glass transition temperature of thecrystallized prepolymer and at which the crystallized prepolymer is in asolid state, to effect solid-state condensation polymerization of thecrystallized prepolymer, thereby increasing the number average molecularweight and the crystallinity of the crystallized prepolymer to from6,000 to 200,000 and at least 35%, respectively, so that the resultantpolycarbonate has a number average molecular weight and a crystallinitywhich are, respectively, greater than those of the crystallizedprepolymer.

In method (B), the pre-polymerization in step (1) may be conducted by aconventional method in which an aromatic dihydroxy compound is reactedwith phosgene in the presence of the above-mentioned molecular weightcontroller, an acid acceptor and a solvent. Preferred examples of acidacceptors include an aqueous alkali solution containing 5 to 10% byweight of an alkali, and a tertiary amine, such as pyridine. Examples ofsolvents include methylene chloride, chloroform, carbon tetrachloride,tetrachloroethylene, chlorobenzene and xylene.

It is preferred that phosgene be added to the reaction system by blowingthe phosgene in gaseous form into a mixture of an aromatic dihydroxycompound, an acid acceptor, a molecular weight controller and a solvent(particularly preferred is methylene chloride), or by dissolvingphosgene in a solvent and dropping the solution into the mixture of anaromatic dihydroxy compound and an acid acceptor. The molecular weightcontroller may be added before, during or after the reaction of phosgenewith an aromatic dihydroxy compound, but it is preferred that themolecular weight controller be added before or during the reaction. Thereaction temperature is generally in the range of from -30° to 100° C.and the reaction time is generally in the range of from 1 minute to 10hours.

The prepolymer prepared by the pre-polymerization in step (1) has anumber average molecular weight of 1,000 to 15,000. This molecularweight can be attained by appropriately selecting reaction conditions,such as the amount of a molecular weight controller, the amount ofaqueous alkali solution, the reaction temperature and the rate of theaddition of phosgene. The prepolymer prepared by the pre-polymerizationgenerally comprises terminal chloroformate groups (--ArOCOCl) andterminal alkali metal-containing phenolate groups (such as --ArONa), inaddition to aryl carbonate groups and hydroxyl groups derived from thearomatic monohydroxy compound used as a molecular weight controller. Theterminal chloroformate groups can be converted to terminal hydroxylgroups by completely hydrolyzing the terminal chloroformate groups intophenolate groups by treatment with an aqueous alkaline solution, andnutralizing the resultant alkali metal-containing phenolate groups withan acid solution, followed by washing with pure water. In the case wherea monohydric alcohol, such as ethanol, or a chloroformate of amonohydric alcohol, such as ethyl chloroformate, is used as a molecularweight controller in combination with an aromatic monohydroxy compound,the terminal groups of the prepolymer are generally comprised of arylcarbonate groups, alkyl carbonate groups, and hydroxyl groups. Preferredis a porous, crystallized aromatic polycarbonate having its terminalgroups comprised substantially of hydroxyl groups and aryl carbonategroups.

The prepolymer obtained by the pre-polymerization in step (1) isgenerally in the form of a solution of the prepolymer in the organicsolvent. The method for obtaining a solid prepolymer from the solutionis not specifically restricted. For example, the prepolymer solution iswell washed and neutralized, and then, (i) the solution is concentratedto dryness, followed by pulverization, or the solution is concentratedto a wet mass, followed by pulverization and drying, to obtain a solid;or (ii) the solution is heated while vigorously stirring and blowingsteam to distill off the solvent.

The solid prepolymer obtained by the above method may have already beenpartly crystallized. However, the prepolymer has not yet be renderedporous and, therefore, its specific surface area is generally as smallas 0.1 m² /g or less. In order to prepare the porous, crystallized,aromatic polycarbonate prepolymer of the present invention from the thusobtained solid prepolymer, the solid prepolymer as such or in a moltenstate is introduced into a solvent and treated with the solvent undersufficient shearing force to crystallize and render porous the amorphousaromatic polycarbonate prepolymer as described above. That is, theprepolymer is treated under shearing force which is sufficient to causethe resultant powdery, porous, crystallized, aromatic polycarbonateprepolymer to have an average particle diameter of 250 μm or less.

Examples of solvents to be used for treating the prepolymer includeacetone, methyl ethyl ketone, methyl propyl ketone, xylene, ethylacetate, acetonitrile and toluene. Of these, acetone is preferred.

The solid-state polymerization in step (3) is conducted as describedhereinbefore in detail. With respect to the solid-state polymerization,it is believed that when the terminal groups of the prepolymer arecomprised not only of terminal phenyl carbonate groups and terminalhydroxyl groups, but also alkyl carbonate groups, such as ethylcarbonate groups, not only advances the condensation polymerizationreaction of the prepolymer while releasing phenol and diphenylcarbonate, but also the polycondensation reaction advances whilereleasing phenyl ethyl carbonate.

Method (C) for producing a crystallized aromatic polycarbonate from anaromatic polycarbonate oligomer and an aromatic dihydroxy compoundcomprises the steps of:

(1) reacting an aromatic polycarbonate oligomer having a number averagemolecular weight of from about 350 to about 950 and having its terminalgroups comprised substantially of aryl carbonate groups with an aromaticdihydroxy compound under heating at a temperature sufficient and for aperiod of time sufficient to prepare an amorphous prepolymer having anumber average molecular weight of from 1,000 to 15,000 and havingterminal hydroxyl and aryl carbonate groups;

(2) treating the amorphous prepolymer with solvent under sufficientshearing force to crystallize to a crystallinity of at least 5% andsimultaneously render porous the prepolymer, the shearing force beingsufficient to cause the resultant powder form of porous, crystallized,aromatic polycarbonate prepolymer to have an average particle diameterof 250 μm or less, the resultant powder form of porous, crystallizedprepolymer having a specific surface area being at least 0.2 m² /g; and

(3) heating the powder form of porous, crystallized prepolymer, orheating an agglomerated powder form or a granular form of porous,crystallized prepolymer derived from the powder form of prepolymer, at atemperature which is higher than the glass transition temperature of thecrystallized prepolymer and at which the crystallized prepolymer is in asolid state, to effect solid-state condensation polymerization of thecrystallized prepolymer, thereby increasing the number average molecularweight and the crystallinity of the crystallized prepolymer to from6,000 to 200,000 and at least 35%, respectively, so that the resultantpolycarbonate has a number average molecular weight and a crystallinitywhich are, respectively, greater than those of the crystallizedprepolymer.

In method (C), an aromatic polycarbonate oligomer having its terminalgroups comprised substantially of aryl carbonate groups is used for thepre-polymerization in step (1). As described above, such an oligomer caneasily be prepared by the transesterification method or the interfacialpolycondensation method.

An agglomerated powder form or a granular form of porous, crystallizedprepolymer, which may be used in step (3) of each of Methods (A), (B)and (C), can easily be obtained individually from the powder form ofporous, crystallized prepolymer in the manner as described before indetail.

The crystallization in step (2) and the solid-state polymerization instep (3) are conducted in the same manner as described hereinbefore indetail.

In all the steps of each of the above methods, i.e., thepre-polymerization, the crystallization of the prepolymer and thesolid-state polymerization, the reaction may be carried out in abatch-wise manner or in a continuous manner. Both the manners may beemployed in combination.

The powder form, the agglomerated powder form or the granular form ofporous, crystallized, aromatic polycarbonate prepolymer of the presentinvention can advantageously be used as a prepolymer to be subjected tosolid-state polymerization to produce a polycarbonate. Further, theprepolymer itself can also be used as a raw material for producing asintered product, a filter, an adsorbent and a coating composition, orcan be mixed with other resins to prepare polymer alloys.

The powder form, the agglomerated form, or the granular form of porous,crystallized, aromatic polycarbonate of the present invention having adesired molecular weight, which is formed by the solid-statepolymerization of the above-mentioned prepolymer, may be directlyintroduced into an extruder without cooling to pelletize it bymelt-extrusion, thereby obtaining colorless, transparent pellets of apolycarbonate. Alternatively, the powder agglomerated powder form orgranular form of porous, crystallized, aromatic polycarbonate may becooled before introducing it into an extruder. Introduction of thepolycarbonate into an extruder without cooling is advantageous from theviewpoints of energy saving in extrusion and increase of the extrusionrate of the extruder. Further, the granular form of polycarbonate hassatisfactorily high bulk density. Therefore, the granular form ofpolycarbonate can be directly subjected to injection molding orextrusion molding without being pelletized by melt-extrusion.Pelletization of a polycarbonate by melt-extrusion not only needs muchenergy but also leads to a lowering of the quality of the aromaticpolycarbonate due to heat deterioration. In the case of the granularform of polycarbonate, pelletization can advantageously be omitted.

According to the present invention, a wide variety of aromaticpolycarbonates, including not only aromatic polycarbonate having a broadmolecular weight distribution, but also aromatic polycarbonate having anarrow molecular weight distribution, can be provided. When a prepolymerhaving a narrow molecular weight distribution is used, an aromaticpolycarbonate having a narrow molecular weight distribution can beobtained. On the other hand, when a prepolymer having a broad molecularweight distribution is used, an aromatic polycarbonate having a broadmolecular weight distribution can be obtained. This is one of theremarkable features of the present invention. As a criterion of themolecular weight distribution, a ratio of a weight average molecularweight (Mw) to a number average molecular weight (Mn), i.e., Mw/Mn, isgenerally used. With respect to a polymer prepared by a condensationpolymerization reaction, there has been established a theory that, whenthe Mw/Mn is 2, the polymer has the narrowest molecular weightdistribution. From the viewpoint of the properties of the polymer, suchas flowability in molding, mechanical strength and elongation, it ispreferred that a polymer have a narrow molecular weight distribution.However, it is practically difficult to prepare a polymer having anMw/Mn of 2.5 or less, particularly not 2.4 or less. In the conventionalpolymerization methods, such as the transesterification method which isknown as a melt process, a polymerization reaction system becomes veryviscous before completion of the polymerization reaction, so that thepolymerization reaction does not advance uniformly. According to thisconventional method, it is infeasible to obtain an aromaticpolycarbonate having a narrow molecular weight distribution. Thearomatic polycarbonate obtained by the conventional transesterificationmethod generally has an Mw/Mn of more than 2.6. In the conventionalphosgene process which is frequently carried out on a commercial scale,the obtained aromatic polycarbonate has an Mw/Mn of from 2.4 to 3.5,generally from 2.5 to 3.2. In contrast, an aromatic polycarbonate havingan Mw/Mn as low as from 2.2 to 2.5 can easily be prepared by the methodof the present invention. The reason for this is believed to be that inthe stage of producing a prepolymer which has a relatively low molecularweight, a prepolymer having a narrow molecular weight distribution caneasily be obtained and such a prepolymer having a narrow molecularweight distribution is used for producing the polycarbonate.

The porous, crystallized, aromatic polycarbonate of the presentinvention, for example, a porous, crystallized, polycarbonate preparedusing bisphenol A, which is one of the most preferred polycarbonates ofthe present invention, is white and opaque. However, when this porous,crystallized, aromatic polycarbonate is heated to a temperature higherthan its crystalline melting point or subjected to melt molding, anamorphous aromatic polycarbonate having good transparency can beobtained. This also is an important feature of the aromaticpolycarbonate of the present invention. When an aromatic polycarbonateis prepared from bisphenol A and diphenyl carbonate by the conventionalmelt process, it is necessary to react highly viscous raw materials witheach other under severe conditions, that is, at a high temperature,i.e., about 300° C., under highly reduced pressure, i.e., 1 mmHg orless, for a prolonged period of time. Consequently, the obtainedpolycarbonate inevitably assumes a light yellow color due to the thermaldecomposition of the polymer or due to the oxidation of the polymer bythe action of a small amount of oxygen present in the reaction system.In contrast, according to the present invention, not only can thepre-polymerization be performed at a relatively low temperature, i.e.,250° C. or less, preferably 240° C. or less, in a short period of timeeven when the transesterification method is employed, but also both thetreatment for crystallization and pore formation and the solid-statepolymerization can be performed at a relatively low temperature, i.e.,230° C. or less. Consequently, in the method of the present invention,there is no danger of deterioration of the polymer, differing from thecase of the conventional melt process, such as the conventionaltransesterification process.

The porous, crystallized, aromatic polycarbonate of the presentinvention may optionally be mixed with various additives such as heatstabilizers, antioxidants, mold release agents, fire retardants andvarious inorganic fillers such as glass fibers, and the resultantcomposition used in a wide variety of fields, such as a engineeringplastics field. Moreover, the porous, crystallized, aromaticpolycarbonate of the present invention can advantageously be kneadedwith another polymer in order to form a polymer alloy. Therefore, theporous, crystallized, aromatic polycarbonate is particularly useful as araw material for the production of a polymer alloy on a commercialscale.

An aromatic polycarbonate containing no chlorine atom can be obtained inthe present invention. The aromatic polycarbonate containing no chlorineatom is extremely useful as a material for an optical instrument and amaterial for electronic equipment.

Further, according to the present invention, it is possible to producenot only an ultra-high molecular weight polycarbonate having a numberaverage molecular weight of 15,000 or more by solid-statepolymerization, which is difficult or impossible to produce by theconventional phosgene method or the conventional transesterificationmethod (melt method), but also a polycarbonate having reactive hydroxylgroups at its terminals.

As aforedescribed, in the conventional phosgene process for producing anaromatic polycarbonate on a commercial scale, by-products includingchlorine and electrolytes, such as sodium chloride, are formed asimpurities. These impurities are disadvantageously and inevitablycontained in the final polycarbonate. Further, a chlorine-containingcompound, such as methylene chloride, which is used as a solvent in alarge amount, is also likely to be contained as an impurity in thepolycarbonate. Such impurities adversely affect the properties of thefinal polycarbonate. Conventionally, in order to decrease the amount ofimpurities contained in the final polycarbonate, washing and otheroperations have been conducted. However, thse operations are troublesomeand expensive, and it is infeasible to remove impurities completely fromthe resin.

By contrast, according to the present invention, even in the mode inwhich the use of phosgene is involved, the product which is obtaineddirectly from phosgene is a prepolymer having a relatively low molecularweight, and such a prepolymer can easily be treated for removingimpurities (such as chlorine-containing compound) therefrom. Therefore,the aromatic polycarbonate of the present invention is completely freefrom such impurities and hence excellent in quality. Moreover,naturally, any troublesome process for removing impurities from thefinal polycarbonate is not required. Accordingly, the method of thepresent invention is commercially advantageous.

Further, in the conventional transesterification melt process, anexpensive reactor is disadvantageously required for attaining a reactionunder high viscosity, high temperature and high vacuum conditions.Therefore, due to the high temperature, the polymer is likely to bedeteriorated. By contrast, according to the method of the presentinvention, such a special reactor is not required, and the aromaticpolycarbonate produced by the method of the present invention hasexcellent properties as described above.

The powder form, the agglomerated powder form or the granular form ofporous, crystallized, aromatic polycarbonate prepolymer can bepolymerized at extremely high reaction rate by solid-statepolymerization, without the danger of adhesion of the prepolymer to theinner wall of the reactor and adhesion between prepolymer particles.Thus, the present invention is extremely useful for providing anaromatic polycarbonate, which can easily, efficiently be produced bysolid-state polymerization on a commercial scale.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference tothe following Examples, which should not be construed as limiting thescope of the present invention.

In the present invention, the molecular weight is expressed in terms ofa number average molecular weight (hereinafter referred to simply as"Mn") and a weight average molecular weight (hereinafter referred tosimply as "Mw") as measured by gel permeation chromatography (GPC). Forreference, the molecular weight of TOUGHLO® A 2500 (registered trademarkof a polycarbonate manufactured and sold by Idemitsu Sekiyukagaku K.K.,Japan) is measured and found to have an Mn of 10,700 and an Mw of28,000.

The molar ratios with respect to terminal groups in a prepolymer and apolycarbonate after solid-state condensation polymerization aredetermined by high-performance liquid chromatography or by nuclearmagnetic resonance (NMR) spectroscopy.

The specific surface area is determined by measuring the surface area ofa sample by means of ACCUSORBR®-2100-02 (manufactured and sold byShimadzu Corp., Japan) using krypton gas, and dividing the measuredsurface area by the weight of the sample.

The average particle diameter of a prepolymer in a solvent forcrystallization is determined by taking an aliquot from a uniformlymixed slurry of the prepolymer, diluting the aliquot with the solvent,applying a ultrasonic wave to the diluted aliquot to disperse theprepolymer in the solvent, casting the resultant dispersion on a glassplate, drying the dispersion to deposit the prepolymer on the glassplate and measuring the particle diameter of the deposited prepolymerusing a microscope.

The particle size distribution of dry particles is determined byclassifying particles into fractions respectively remaining on 1,070 μmscreen, 850 μm screen, 600 μm screen, 250 μm screen, 150 μm screen, 75μm screen and 50 μm screen and a fraction passing through 50 μm screenby means of micro-type magnetic vibration screen classifier model M-2(manufactured and sold by Tsutsui Rikagaku Kiki, Japan), and measuringthe weight of each of the fractions.

The crystallinity is measured by the X ray diffractometry as describedhereinbefore.

In Examples 18 to 24, the compressive break strength of a granularprepolymer and a granular polycarbonate after solid-state condensationpolymerization is determined as follows. That is, using, for example, aKiya type hardness meter, a compressive force is applied betweenopposite surfaces of a sample, which each have an area of at least about1 mm² and are apart from each other substantially in parallelrelationship at a distance of about 1 mm. The load for application of acompressive force is increased until the sample breaks. The load(kgf/cm²) at which the sample breaks is referred to simply as the loadat break. The measurement of the load at break is conducted 10 times.When a sample prepolymer or polycarbonate does not have two surfaceswhich are apart from each other substantially in parallel relationship,a sample having such opposite surfaces is cut out from the originalsample, followed by measurement of compressive break strength in themanner described above. From the 10 values of load at break thusobtained, the maximum and minimum values are omitted, and the average ofthe remaining 8 values is calculated. The compressive break strength isrepresented by the calculated average value.

In Examples 33 and 34, the compressive break strength (kgf/cm²) ismeasured using an Instron type universal tester.

The partial pressure of phenol in a phenolsaturated nitrogen gas used insolid-state condensation polymerization is determined from the vaporpressure of phenol calculated according to the following formula shownon page 128 of Kagaku Binran II (Handbook of Chemistry) (published in1984 by Maruzen Co., Japan). ##EQU4## [wherein P represents a vaporpressure of phenol (mmHg) and t represents a temperature (° C.)].

In the following Examples, porous, crystallized, aromatic polycarbonateprepolymer is often referred to simply as "porous, crystallizedprepolymer"; amorphous, aromatic, polycarbonate prepolymer is oftenreferred to simply as "amorphous prepolymer"; porous, crystallized,aromatic polycarbonate is often referred to simply as "porous,crystallized polycarbonate"; shaped, porous, crystallized, aromaticpolycarbonate is often referred to simply as "shaped, porous,crystallized polycarbonate"; and granular, porous, crystallized,aromatic polycarbonate is often referred to simply as "granular, porous,crystallized polycarbonate".

Example 1

13.0 kg of 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as"bisphenol A") and 13.4 kg of diphenyl carbonate are charged into a 40 lglass-lined reactor provided with a stirrer, a gas inlet and a gasoutlet. The resultant mixture is melted by heating to 180° C. anddegassing is conducted under reduced pressure, followed by heating to230° C. over a period of 3 hours. During the the temperature elevation,nitrogen gas is flowed through the reactor so that evaporated phenol isdischarged from the reactor. Simultaneously with the termination of thetemperature elevation, introduction of nitrogen gas is terminated. Then,the pressure in the reactor is stepwise reduced to 1 mmHg over a periodof 2 hours. During the period of the pressure reduction, by-producedphenol and diphenyl carbonate are continuously discharged from thereactor. The reaction is further continued for 2 hours under reducedpressure of 1 mmHg to obtain about 10 kg of an amorphous prepolymerhaving a number average molecular weight of 4,000 and a molar ratio ofterminal hydroxyl groups to terminal phenyl carbonate groups of 33/67[hereinafter referred to as "amorphous prepolymer (I)"]. About 10 kg ofmolten amorphous prepolymer (I) is extruded in a strand form at about240° C. over a period of 1 hour through a die having 40 orifices of 1 mmin diameter into a Waring blender type acetone bath filled with 15 kg ofacetone having a temperature of from 40° to 50° C. Simultaneously withthe extrusion, the blender in the acetone bath is revolved at a rate ashigh as 1,000 rpm so that the extruded strand is drawn and stretchedinto a thin fiber. The thin fiber is dipped in the acetone bath, andexposed to strong shearing force by agitation, thereby beingcrystallized, rendered porous and reduced to particles. As a result,particles of a porous, crystallized prepolymer are formed. The thusformed particles in acetone have an average particle v diameter of 150μm. Then, acetone is distilled off under reduced pressure while heatingthe acetone bath to dry the porous, crystallized prepolymer. The thusobtained porous, crystallized prepolymer is white and opaque. When thesurface of the porous, crystallized prepolymer is observed by means of ascanning electron micrograph, it is confirmed that a large number ofpores are present on the surface of the crystallized prepolymer [seeFIG. 1 (3060×magnification)]. On the other hand, when a relatively largeparticle (about 800 μm in diameter) of the porous, crystallizedprepolymer is broken with forceps and the resultant section of particleof the porous, crystallized prepolymer is observed by means of ascanning electron micrograph, it is confirmed that a large number ofpores are also present on the section [see FIG. 2 (1020×magnification)].For the purpose of comparison, melted amorphous prepolymer (I) is cooledto room temperature and the surface of the cooled amorphous prepolymer(I) is observed by means of a scanning electron micrograph. As a result,it is confirmed that the surface of the amorphous prepolymer (I) issmooth and has no pore [see FIG. 3 (4400×magnification)].

The above-obtained porous, crystallized prepolymer has a specificsurface area of 1.5 m² /g and a crystallinity of 28%.

10 kg of the porous, crystallized prepolymer is charged into acylindrical, gas flow type reactor made of stainless steel (internaldiameter: 60 cm, height: 1 m) which is provided, at its bottom portion,with a sintered filter having pores of from about 40 to about 50 μm indiameter and having a thickness of about 5 mm, and heated to 180° C.,followed by solid-state condensation polymerization. During thesolid-state condensation polymerization, heated nitrogen gas isuniformly introduced at a rate of 10 m³ (N.T.P.)/hr from the bottomportion of the reactor through the sintered filter, and discharged fromthe upper portion of the reactor. The temperature of the polymerizationis regulated by controlling the temperature of the heated nitrogen gas.The temperature is elevated from 180° C. to 220° C. at a temperatureelevation rate of 10° C./hr and then kept at 220° C. for 5 hours,thereby obtaining a porous, crystallized polycarbonate having an Mn of13,000 and an Mw of 31,200. The porous, crystallized polycarbonate has aspecific surface area of 0.8 m^(2/) g and a crystallinity of 45%. A DSCchart [obtained using a DSC analyzer (model DSC7 manufactured and soldby Perkin Elmer Co., U.S.A.); the ordinate of the chart indicates heatflow (mW) while the abscissa indicates temperature (°C.)] of the porous,crystallized polycarbonate is shown in FIG. 9, in which the peakexhibiting the melting point of the polycarbonate appears at 271° C.From the charat, it is found that the half-width is 4.3° C. To theobtained porous, crystallized polycarbonate is added 250 ppm oftris(nonylphenyl) phosphite as a heat stabilizer, and melt-extrusion isconducted at 280° C. to obtain a colorless, transparent, amorphouspolycarbonate. When the amorphous polycarbonate is injection-molded at300° C., no silver streak occurs. With respect to the color of theresultant shaped article, the L-value and b*-value measured using acolor and color-difference meter Model CR-200b (Minolta Camera Co.,Ltd., Japan) are 91.7 and 3.5, respectively, i.e., the shaped article iscolorless and transparent.

EXAMPLE 2

10 kg of amorphous prepolymer (I) prepared in substantially the samemanner as in Example 1 is melted and extruded at about 240° C. and thencooled with water. After the cooling, pelletization is conducted. Theresultant amorphous pellets are pulverized using a plastics pulverizer(manufactured by Fritsch Co., West Germany) to obtain a powder having adiameter of 1 mm or less.

An acetone bath as used in Example 1 is filled with 15 kg of acetone andacetone is kept at 40° C. Into the acetone bath is gradually charged theabove obtained powder over a period of 1 hour while stirring at the samerate as in Example 1, i.e., 1,000 rpm to effect crystallization and poreformation. The resultant porous, crystallized prepolymer in acetone hasan average particle diameter of 180 μm. Then, acetone is distilled offin substantially the same manner as in Example 1 to dry the porous,crystallized prepolymer. The scanning electron micrographs withmagnifications of 1020, 3060 and 6020, respectively, of the surface ofthe thus obtained porous, crystallized prepolymer are respectively shownin FIGS. 4 to 6. It is confirmed from FIGS. 4 to 6 that the porous,crystallized prepolymer has pores having substantially uniformdiameters. The porous, crystallized prepolymer has a specific surfacearea of 1.2 m² /g and a crystallinity of 26%.

The above-obtained porous, crystallized prepolymer is subjected tosolid-state condensation polymerization in substantially the same manneras in Example 1 to obtain a porous, crystallized polycarbonate having anMn of 12,500 and an Mw of 29,600. When the porous, crystallizedpolycarbonate is injection-molded in substantially the same manner as inExample 1, the same colorless and transparent shaped article having nosilver streak as obtained in Example 1 is obtained.

EXAMPLE 3

10 kg of amorphous prepolymer pellets (about 2 mm in diameter, about 3mm in length) prepared in substantially the same manner as in Example 2,without pulverization, are charged into an acetone bath filled with 15kg of acetone over a period of 1 hour while stirring to effectcrystallization. The resultant porous, crystallized prepolymer inacetone has an average particle diameter of 230 μm. Then, acetone isdistilled off in substantially the same manner as in Example 1 to drythe porous, crystallized prepolymer. The thus obtained porous,crystallized prepolymer has a particle diameter larger than that of theporous, crystallized prepolymer obtained in Example 2 (whilst someportion of the porous, crystallized prepolymer maintains substantiallythe same size as that of the starting pellet). The porous, crystallizedprepolymer is less white and assumes slight transparency, as compared tothe porous, crystallized prepolymer obtained in Example 2. The porous,crystallized prepolymer has a specific surface area of 0.4 m² /g and acrystallinity of 23%.

The porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 2 except that the period of time for which the temperature iskept at 220° C. is changed to 14 hours, thereby obtaining a porous,crystallized polycarbonate having an Mn of 13,000 and an Mw of 31,400.In this Example, a longer polymerization time is required than inExamples 1 and 2.

COMPARATIVE EXAMPLE 1

10 kg of amorphous prepolymer powder prepared in substantially the samemanner as in Example 2 is dissolved in 100 l of methylene chloride andthen, methylene chloride is distilled off at room temperature underreduced pressure. Then, the resultant powder is placed in a vacuumdrier, and dried at 40° C. overnight to obtain a powder having acrystallinity of 25% and a specific surface area of 0.07 m² /g. Thecrystallized prepolymer powder is subjected to solid-state condensationpolymerization in substantially the same manner as in Example 1 exceptthat polymers being formed are sampled 8 hours, 13 hours and 24 hoursafter the initiation of the polymerization at 220° C. From themeasurement of the molecular weight of each of the samples, it is foundthat the number average molecular weight of the polycarbonate reaches8,100, 8,900 and 9,200 at respective polymerization times of 8, 13 and24 hours. No significant further increase is observed in the numberaverage molecular weight of the polycarbonate, and the desired numberaverage molecular weight, i.e., Mn=12,500 cannot be attained.Polycarbonate having an Mn of 12,500 corresponds to a commerciallyavailable aromatic polycarbonate resin of the grade classified as highviscosity grade. The process which cannot provide a polycarbonate havingan Mn of 12,500, is commercially disadvantageous.

COMPARATIVE EXAMPLE 2

10 kg of amorphous prepolymer powder prepared in substantially the samemanner as in Example 2 is placed in an atmosphere of tetrahydrofuranvapor-saturated nitrogen gas at about 40° C. for 24 hours to effectcrystallization. The resultant crystallized prepolymer has a specificsurface area of 0.05 m² /g and a crystallinity of 20%.

The crystallized prepolymer is subjected to solid-state condensationpolymerization in substantially the same manner as in Example 1 exceptthat the period of time for which the temperature is kept at 220° C. ischanged to 24 hours. As in Comparative Example 1, the number averagemolecular weight of the polycarbonate cannot be increased to a desiredlevel. The obtained polycarbonate has an Mn of 8,800.

COMPARATIVE EXAMPLE 3

10 kg of 2,2-bis [(4-methyl carbonate)phenyl] propane is charged intothe same reactor as used in Example 1, and stirred while introducing dryargon gas heated to 280° C. at a flow rate of 30 l(N.T.P.)/hr to effectreaction at 280° C. for 7 hours, thereby obtaining an amorphousprepolymer having an Mn of 1,700 and an Mw of 3,300. The prepolymer istreated with methylene chloride to effect crystallization, and thendried in substantially the same manner as in Comparative Example 1.Thereafter, the resultant crystallized prepolymer is subjected tosolid-state condensation polymerization in substantially the same manneras in Example 1 except that polymers being formed are sampled 24 hoursand 50 hours after the initiation of the polymerization at 220° C. Fromthe measurement of the molecular weight of each of the samples, it isfound that the number average molecular weight reaches 6,500 (Mw=16,800)and 7,100 (Mw=18,000) at respective polymerization times of 24 and 50hours. The molecular weight of the polycarbonate cannot be increased toa desired level.

COMPARATIVE EXAMPLE 4

Polymerization for obtaining an amorphous prepolymer(pre-polymerization) is conducted in substantially the same manner as inComparative Example 3, except that 3 g of dibutyltin oxide is used as acatalyst and that the polymerization temperature and polymerization timeare changed to 250° C. and 6 hours, to obtain an amorphous prepolymerhaving an Mn of 3,100 and an Mw of 6,400. The amorphous prepolymer iscrystallized with methylene chloride, and then dried in substantiallythe same manner as in Comparative Example 1. Then, the resultantcrystallized prepolymer is subjected to solid-state condensationpolymerization in substantially the same manner as in Example 1 exceptthat polymers being formed are sampled 24 hours and 40 hours after theinitiation of the polymerization at 220° C. From the measurement of themolecular weight of each of the samples, it is found that the numberaverage molecular weight of the polycarbonate reaches 8,500 and 10,300at respective polymerization times of 24 and 40 hours. When thepolycarbonates having Mn's of 8 500 and 10,300 are individuallyinjection-molded at 300° C. to prepare shaped articles, silver streaksmarkedly occur on each of the shaped articles, and the surface of eachof the shaped articles has hazy, opaque portions.

EXAMPLE 4

10 kg of an amorphous polycarbonate prepolymer having a number averagemolecular weight of 3,900 and a molar ratio of terminal hydroxyl groupsto terminal phenyl carbonate groups of 35/65, which is prepared insubstantially the same manner as in Example 1 except that, in thepolymerization step, the temperature is elevated to 250° C. and kept at235° C. is melted by heating at about 240° C. and extruded in a thinstrand form, over a period of 1 hour, into a Waring blender acetone bathfilled with 12 kg of acetone having a temperature of 40° to 50° C.through a die having 40 orifices of 1 mm in diameter. Simultaneouslywith the extrusion, the acetone and the prepolymer are agitated with astirrer provided with blades at a rate as high as 500 rpm to effectcrystallization and pore formation while effecting reduction of theprepolymer to fine powder. The resultant acetone slurry of a porous,crystallized prepolymer is opaque, and it is found that a great numberof fine particles are present in the acetone slurry. The thus formedparticles in acetone have an average particle diameter of 180 μm. Whenthe acetone slurry is allowed to stand, a porous, crystallizedprepolymer precipitates so that the upper portion of the acetonesolution becomes transparent. When a portion of the transparent upperportion is taken out and the acetone contained therein is distilled off,a polycarbonate oligomer having a number average molecular weight of 710is obtained. From the amount of the portion taken out and the amount ofthe oligomer obtained, it is found that the oligomer is present in theacetone solution in an amount of 390 g per 12 kg of acetone.

The acetone slurry of the porous, crystallized prepolymer is heatedwhile stirring to distill off the acetone, so that the porous,crystallized prepolymer is dried. The particle diameter distribution ofthe thus obtained porous, crystallized prepolymer is measured. Afraction of the porous, crystallized prepolymer which passes through 50μm screen is 2.8% by weight, based on the weight of the porous,crystallized prepolymer, and fractions of the porous, crystallizedprepolymer which remain on 50 μm screen, 75 μm screen, 150 μm screen,250 μm screen, 600 μm screen, 850 μm screen and 1070 μm screen arerespectively 3.4% by weight, 12.6% by weight, 11.7% by weight, 20.7% byweight, 26.8% by weight, 15.4% by weight and 6.5% by weight, based onthe weight of the porous, crystallized prepolymer. Since thepolycarbonate oligomer serves as an adhesive during the drying,agglomeration of the powder of the porous, crystallized prepolymeroccurs to form secondary particles, leading to a large particlediameter. The porous, crystallized prepolymer has a specific surfacearea of 1.7 m² /g and a crystallinity of 29%.

9 5 kg of the porous, crystallized prepolymer (which has preliminarilybeen heated to 140° C.) is subjected to solid-state condensationpolymerization using a 70 l tumbler type, solid-state condensationpolymerization reactor made of a stainless steel. The solid-statecondensation polymerization is conducted under conditions such thatnitrogen gas is introduced little by little into the reactor whilekeeping the pressure at 1 to 2 mmHg using a vacuum pump and that thetemperature is elevated from 140° C. to 180° C. over 30 minutes andfurther elevated from 180° C. to 220° C. at a rate of 10° C./hr, andthen kept at 220° C. for 7 hours, thereby obtaining a porous,crystallized polycarbonate having an Mn of 11,500. There is observed noadhesion of the polycarbonate to the inner wall of tumbler, and observedalmost no adhesion of the polycarbonate to a bag filter disposed betweenthe tumbler and the vacuum pump. The porous, crystallized polycarbonateobtained by the solid-state condensation polymerization is melted,extruded and pelletized at 280° C. to obtain colorless, transparentpellets of an amorphous aromatic polycarbonate. The thus obtainedpellets is injection-molded at 300° C. to obtain a plate. The plateexhibits a transmittance (according to ASTM D1003) of 90.4% and a haze(according to ASTM D1003) of 0.3%.

EXAMPLE 5

An acetone slurry of a porous, crystallized prepolymer obtained insubstantially the same manner as in Example 4 is separated into theporous, crystallized prepolymer and an acetone solution by means of abatch type centrifugal separator. 9 kg of the thus obtained porous,crystallized prepolymer and a separately prepared 650 g of an acetonesolution of a polycarbonate oligomer having an Mn of 850 (oligomerconcentration: 30% by weight) are mixed well, and acetone is distilledoff while heating and stirring, to obtain a dried, porous, crystallizedprepolymer. The particle diameter distribution of the thus obtainedporous, crystallized prepolymer is determined by classifying theparticles into fractions by means of screens The major fraction is onecontaining the particles of the prepolymer having passed through the 600μm screen. The amount of the prepolymer contained in the fraction havingpassed through the 50 μm screen is only 3 5% by weight, based on thetotal weight of the prepolymer The porous, crystallized prepolymer has aspecific surface area of 1.5 m² /g and a crystallinity of 28%.

The porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 4 to obtain a porous, crystallized polycarbonate having Mn of10,800, a specific surface area of 0.8 m² /g and a molar ratio ofterminal hydroxyl groups to terminal phenyl carbonate groups of 4/96.

Neither adhesion of the polycarbonate to the inner wall of tumbler norclogging of the bag filter with the polycarbonate is observed.

EXAMPLE 6

An amorphous prepolymer having a number average molecular weight of5,100 and a molar ratio of terminal hydroxyl groups to terminal phenylcarbonate groups of 30/70 is prepared in substantially the same manneras in Example 1 except that the period of time for keeping the pressureat 1 mmHg is changed to 3 hours. The amorphous prepolymer is subjectedto solid-state condensation polymerization in substantially the samemanner as in Example 4 to obtain a porous, crystallized prepolymerhaving a specific surface area of 1.3 m² /g. The particle diameterdistribution of the thus obtained porous, crystallized prepolymer, whichis determined by classifying of the particles into fractions by means ofscreens, is such that the major fraction is one containing the particlesof the prepolymer having passed through the 850 μm screen. The amount ofthe particles contained in the fraction having passed through the 50 μmscreen is 1.3% by weight, based on the total weight of the prepolymer.

The porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 4 except that the period of time for keeping the prepolymer at220° C. is changed to 6 hours, thereby obtaining a porous, crystallizedpolycarbonate having Mn of 10,200, a crystallinity of 41%, a crystallinemelting point of 262° C. and a specific surface area of 0.6 m² /g.Neither adhesion of the polycarbonate to the inner wall of tumbler norclogging of the bag filter with the polycarbonate is observed.

EXAMPLE 7

An aqueous solution prepared by dissolving 64.8 g of sodium hydroxide in800 g of water, is mixed with 137 g of bisphenol A, 400 ml of methylenechloride and 1.7 g of phenol to prepare an emulsion. Into the emulsionis gradually blown 58.5 g of phosgene over a period of 1 hour whilestirring and while maintaining the temperature at from 10° to 20° C., toadvance a reaction. To the resultant reaction mixture is added 0.12 g oftriethylamine, followed by stirring for 1 hour, thereby separate themixture into a methylene chloride layer (a prepolymer solution inmethylene chloride) and an aqueous layer. The methylene chloride layeris collected, and to the methylene chloride layer is added an aqueoussodium hydroxide solution to convert the remaining chloroformate groupsinto phenolate groups, followed by neutralization with phosphoric acidand by sufficient washing with water. From the resultant solution of theprepolymer in methylene chloride, the methylene chloride is distilledoff, followed by drying overnight using a vacuum dryer. The resultantdried prepolymer is pulverized in substantially the same manner as inExample 2 and then charged in a small size Waring blender containing 300g of acetone while stirring at 1,000 rpm, thereby effectingcrystallization and pore formation of the prepolymer. Then, acetone isdistilled off to dryness to obtain a dried, porous, crystallizedprepolymer. The thus obtained porous, crystallized prepolymer has an Mnof 2,300, an Mw of 4,600, a crystallinity of 28%, a specific surfacearea of 1.3 m² /g and a molar ratio of terminal hydroxyl groups toterminal phenyl carbonate groups of 45/55. The analysis of chlorine bypotentiometric titration and atomic absorption shows that anychlorine-containing compound is not contained in this polymer.

Then, the porous, crystallized prepolymer (which has preliminarily beenheated to 140° C.) is subjected to solid-state condensationpolymerization using a rotary evaporator under conditions such that thepressure is in the range of from 2 to 3 mmHg and that the temperature iselevated from 140° C. to 180° C. over 10 minutes and further elevatedfrom 180° C. to 220° C. at a temperature elevation rate of 10° C./hr,and then kept at 220° C. for 4 hours, thereby obtaining a porous,crystallized polycarbonate having number average molecular weight of9,500 and a specific surface area of 0.5 m² /g.

EXAMPLE 8

An aqueous solution prepared by dissolving 62 g of sodium hydroxide in800 g of water, is mixed with 137 g of bisphenol A, 400 ml of methylenechloride and 1.7 g of phenol to prepare an emulsion. Into the emulsionis gradually blown 55 g of phosgene over a period of 1 hour whilestirring and maintaining the temperature at from 10° to 20° C. Into theresultant reaction mixture is blown 6 g of phosgene over a period of 5minutes. To the mixture, 0.13 g of triethylamine is added, followed bystirring for 1.5 hours. Then, the mixture is subjected to separation ofthe methylene chloride layer from the aqueous layer and, then, topurification, and subsequently subjected to crystallization and poreformation in substantially the same manner as in Example 7, therebyobtaining a porous, crystallized prepolymer. The thus obtained porous,crystallized prepolymer has an Mn of 3,300, an Mw of 6,500, acrystallinity of 28%, a specific surface area of 1.0 m² /g and a molarratio of terminal hydroxyl groups to terminal phenyl carbonate groups of40/60.

The porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 7, thereby obtaining a porous, crystallized polycarbonate havinga weight average molecular weight of 25,000 (Mw/Mn=2.3) and a specificsurface area of 0.5 m² /g.

EXAMPLE 9

Pre-polymerization is conducted in substantially the same manner as inExample 1 except that 13 kg of bisphenol A and 13 kg of diphenylcarbonate are used, thereby obtaining 12 kg of an amorphous prepolymerhaving an Mn of 3,200 and a molar ratio of terminal hydroxyl groups toterminal phenyl carbonate groups of 50/50. From the bottom portion ofthe pre-polymerization reactor, 10 kg of the molten amorphous prepolymerat about 240° C. is extruded into an acetone bath filled with 15 kg ofacetone from the upper portion of the acetone bath through a die having40 orifices of 1 mm in diameter over a period of 1 hour. The bottomportion of the acetone bath is connected with a suction port of acentrifugal pump provided with cutter blades (tradename: Santoku CutterPump, Model SD-K, manufactured and sold by Sanwa Tokushu Seiko Co.,Japan) through a pipe, and a delivery port of the pump is connected witha side portion of the acetone bath through a pipe. By operating thecentrifugal pump provided with cutter blades, the contents of theacetone bath are circulated through the acetone bath and the pump. Whenpassed through the pump, the prepolymer is reduced to fine powder by theaction of the cutter blades rotating at a high rate. An acetone slurrycontaining a porous, crystallized prepolymer is obtained by extrudingthe prepolymer into acetone while operating the pump. The porous,crystallized prepolymer in the acetone slurry has an average particlediameter of 190 μm. Acetone is distilled off from the acetone slurry insubstantially the same manner as in Example 1 to dry the porous,crystallized prepolymer. The thus obtained porous, crystallizedprepolymer has a specific surface area of 1.9 m² /g and a crystallinityof 31%. Scanning electron micrographs of the porous prepolymer withmagnifications of 3,060 and 6,020 are respectively shown in FIGS. 7 and8.

The porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 1 except that the temperature is elevated to 230° C. and kept at230° C. for 10 hours, thereby obtaining a porous polycarbonate having anultra-high molecular weight, i.e., an Mn of 26,000 and an Mw of 65,000.After keeping the temperature at 230° C. for 10 hours, the temperatureis further elevated to 240° C. and kept at 240° for 10 hours, therebyobtaining a porous, crystallized polycarbonate having an ultra-highmolecular weight, i.e., an Mn of 40,000 and Mw of 100,000.

EXAMPLE 10

Pre-polymerization, crystallization and solid-state condensationpolymerization are conducted in substantially the same manner as inExample 1 except that 6.5 kg of bisphenol A and 13.3 kg of2,2-bis[(4-phenyl carbonate)phenyl] propane ##STR19## are used in placeof 13.0 kg of bisphenol A and 13.4 kg of diphenyl carbonate. By thepre-polymerization and the crystallization, a porous, crystallizedprepolymer having an Mn of 2,500, a specific surface area of 0.8 m² /g,a crystallinity of 31% and a molar ratio of terminal hydroxyl groups toterminal phenyl carbonate groups of 42/58 is obtained. By thesolid-state condensation polymerization, a porous, crystallizedpolycarbonate having an Mn of 13,000 is obtained.

EXAMPLE 11

Pre-polymerization and crystallization are conducted in substantiallythe same manner as in Example 1 except that the amount of diphenylcarbonate is changed to 12.1 kg to obtain a porous, crystallizedprepolymer having Mn of 4,300, a specific surface area of 1.5 m² /g, acrystallinity of 30% and a molar ratio of terminal hydroxyl groups toterminal phenyl carbonate groups of 65/35. The porous, crystallizedprepolymer is subjected to solid-state condensation polymerization insubstantially the same manner as in Example 1 to obtain a porous,crystallized polycarbonate having an Mn of 12,300 and a molar ratio ofterminal hydroxyl groups to terminal phenyl carbonate groups of 98/2.That is, the terminals of the obtained porous, crystallizedpolycarbonate are substantially hydroxyl groups. Incidentally, when theporous, crystallized polycarbonate is reacted , while heating, withglycidyl polyether, which is prepared from bisphenol A andepichlorohydrin, in the presence of triethylenetetramine as a curingagent, a cured product which is insoluble in tetrahydrofuran isobtained.

EXAMPLE 12

An aqueous solution prepared by dissolving 64.8 g of sodium hydroxide in800 g of water, is mixed with 137 g of bisphenol A, 400 ml of methylenechloride and 1.7 g of phenol to prepare an emulsion. Into the emulsionis gradually blown 58.5 g of phosgene over a period of 1 hour whilestirring and maintaining the temperature at 10° to 20° C. to advance areaction. To the resultant reaction mixture is added a solution preparedby dissolving 0.8 g of ethyl chloroformate in 40 ml of methylenechloride. To the mixture, 6 g of phosgene is blown over a period of 5minutes and 0.15 g of triethylamine is added, followed by stirring for 2hours. Then, the resultant mixture is subjected to separation of amethylene chloride layer from an aqueous layer and, then, topurification, and subsequently subjected to crystallization and poreformation in substantially the same manner as in Example 7. Thus, aporous, crystallized prepolymer is obtained. The obtained porous,crystallized prepolymer has an Mn of 3,000, an Mw of 6,300, a specificsurface area of 1.3 m² /g, a crystallinity of 25% and a molar ratio ofthe total of terminal hydroxyl groups and terminal ethyl carbonategroups (molar ratio of terminal hydroxyl groups to terminal ethylcarbonate groups is 26/23) to terminal phenyl carbonate groups of 49/51.

The porous, crystallized prepolymer is charged in a rotary evaporatorprovided with a heating oven at 180° C., then heated from 180° C. to220° C. at a temperature elevation rate of 5° C./hr, and kept at 220° C.for 4 hours while rotating the evaporator under reduced pressure of from2 to 3 mmHg while introducing dry nitrogen little by little to advance areaction, thereby obtaining a porous, crystallized polycarbonate havinga weight average molecular weight of 24,000 (Mw/Mn=2.2) and a specificsurface area of 0.6 m2/g.

EXAMPLE 13

An aqueous solution prepared by dissolving 58 g of sodium hydroxide in800 g of water, is mixed with 124 g bisphenol A, 400 ml of methylenechloride and 1.2 g of phenol to prepare an emulsion. Into the emulsionis gradually blown 53 g of phosgene over a period of 1 hour whilestirring and maintaining the temperature at 10° to 20° C. to advance areaction. Into the resultant reaction solution is further blown 6 g ofphosgene over a period of 5 minutes. To the mixture, 0.15 g oftriethylamine is added, followed by stirring for 2 hours. Then, theresultant mixture is subjected to separation of an ethylene chloridelayer from an aqueous layer and, then, to purification, and subsequentlysubjected to crystallization and pore formation in substantially thesame manner as in Example 7. Thus, a porous, crystallized prepolymer isobtained. The porous, crystallized prepolymer has an Mn of 9,100, acrystallinity of 21%, a specific surface area of 0.8 m² /g and a molarratio of terminal hydroxyl groups to terminal phenyl carbonate groups of40/60.

The porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 7 except that the period of time for keeping the prepolymer at220° C. is changed to 5 hours, to thereby obtain a porous, crystallizedpolycarbonate having an Mn of 11,200 and a specific surface area of 0.3m² /g.

EXAMPLE 14

148 g of bisphenol, 1.4 g of p-tert-butyl phenol, 0.8 g of phenol, 0.50g of methanol, 162 g of dry pyridine and 600 ml of methylene chlorideare charged in a flask and 65 g of phosgene is blown into the flask overa period of 90 minutes while stirring and maintaining the temperature at10° to 20° C. Then, 400 ml of methylene chloride is additionally chargedin the flask and 50 ml of methylene chloride containing 5 g of phosgeneis dropwise added while stirring and a reaction is advanced for 90minutes. Then, the resultant reaction mixture is added to 900 ml of 10%by weight hydrochloric acid, followed by sufficiently stirring.Thereafter, the resultant mixture is subjected to separation of amethylene chloride layer from an aqueous layer and, then, topurification, and subsequently subjected to crystallization and poreformation in substantially the same manner as in Example 7. Thus, aporous, crystallized prepolymer is obtained. The porous, crystallizedprepolymer has an Mn of 3,600, a crystallinity of 23%, a specificsurface area of 1.8 m² /g and a molar ratio of the total of terminalhydroxyl groups and terminal methyl carbonate groups (molar ratio ofterminal hydroxyl groups to terminal methyl carbonate groups is 16/36)to terminal aryl carbonate groups (terminal p-tert-butylphenyl carbonategroups and terminal phenyl carbonate groups) of 52/48.

Then, the porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 12 except that the period of time for keeping the prepolymer at220° C. is changed to 10 hours, thereby obtaining a porous, crystallizedpolycarbonate having a weight average molecular weight of 24,000(Mw/Mn=2.5).

EXAMPLE 15

An aqueous solution prepared by dissolving 60 g of sodium hydroxide in850 g of distilled water is mixed with 146 g of bisphenol A, 400 ml ofmethylene chloride and 1.7 g of phenol to prepare an emulsion. Into theemulsion is gradually blown 62 g of phosgene at a temperature of from10° to 20° C. over a period of 1 hour while stirring to effect reaction.Then, a solution prepared by dissolving 1.3 g of terephthaloyl chloridein 160 ml of methylene chloride is added to the reaction mixture.Thereafter, 6.4 g of phosgene is blown into the reaction mixture and, 10minutes after completion of the blowing, 0.16 g of triethylamine isadded thereto. The reaction mixture is stirred for 1 hour.

From the reaction mixtures, a layer of methylene chloride containing aprepolymer is separated. The layer is washed with 0.1N hydrochloric acidand then with water.

Added to the thus obtained methylene chloride solution of the prepolymeris 10 ppm of a disodium salt of bisphenol A. The methylene chloridesolution of the prepolymer is subjected to distillation-off of themethylene chloride therefrom and then subjected to crystallization insubstantially the same manner as in Example 7, to obtain a porous,crystallized prepolymer. The thus porous, crystallized prepolymer has anumber average molecular weight of 3,200, a weight average molecularweight of 6,500, a crystallinity of 25%, and a specific surface area of1.0 m² /g. The porous, crystallized prepolymer is subjected tosolid-state condensation polymerization in substantially the same manneras in Example 12, to obtain a porous, crystallized polycarbonate havinga weight average molecular weight of 33,000 (Mw/Mn=2.4).

EXAMPLE 16

An aqueous solution prepared by dissolving 64.8 g of sodium hydroxide in800 g of distilled water is mixed with 137 g of bisphenol A, 400 ml ofmethylene chloride and 1.7 g of phenol to prepare an emulsion. Into theemulsion is gradually blown 58.5 g of phosgene at a temperature of from10° to 20° C. over a period of 2 hours while stirring to advancereaction.

Then, 6 g of phosgene is blown into the reaction mixture over a periodof 5 minutes. 0.15 g of triethylamine is added to the reaction mixture,and stirred for two hours. The reaction mixture is subjected topurification and then subjected to crystallization in substantially thesame manner as in Example 7, to obtain a porous, crystallizedprepolymer. The porous, crystallized prepolymer has a number averagemolecular weight of 3,300, a weight average molecular weight of 6,500, acrystallinity of 28% and a specific surface area of 1.0 m² /g, and amolar ratio of terminal hydroxyl groups to terminal phenylcarbonategroups of 40:60. 100 g of porous, crystallized prepolymer is chargedinto a glass-made gas flow type reactor of 50 mm in inner diameterhaving a glass filter (pore size: about 40-50 μm) attached to one endthereof. Nitrogen gas is fed into the reactor through the glass filterat a gas flow rate of 120 liters (N.T.P.)/hour, and solid-statecondensation polymerization is performed at 210° C. under atmosphericpressure for a period of three hours. Thus, there is obtained a porous,crystallized polycarbonate having a weight average molecular weight of25,000 (Mw/Mn=2.3) and a specific surface area of 0.5 m² /g.

EXAMPLE 17

An aqueous solution prepared by dissolving 64.8 g of sodium hydroxide in800 g of water is mixed with 137 g of bisphenol A, 400 ml of methylenechloride and 18 g of phenol to prepare an emulsion. Into the emulsion isgradually blown 58.5 g of phosgene at a temperature of from 10° to 20°C. over a period of 1 hour while stirring to effect reaction. Further, 6g of phosgene is blown into the reaction mixture over a period of 5minutes, and 0.15 g of triethylamine is added thereto. The reactionmixture is stirred for two hours. A layer of methylene chloride isseparated. The separated layer is neutralized with phosphoric acid, andthen sufficiently washed with water. After distilling off the methylenechloride, the remainder is vacuum-dried to obtain an oligomer having amolar ratio of terminal hydroxyl groups to terminal phenyl carbonategroups of 2:98. The oligomer has a number average molecular weight of800. 28.4 g of bisphenol A is mixed with 100 g of the oligomer. Theresultant mixture is subjected to melt polymerization at 230° C., andthen subjected to crystallization in substantially the same manner as inExample 2, to obtain a porous, crystallized prepolymer having a numberaverage molecular weight of 3,800,a specific surface area of 0.9 m² /gand a molar ratio of terminal hydroxyl groups to terminal phenylcarbonate groups of 58:42. The analysis of this prepolymer shows thatany chlorine-containing compound is not contained in the prepolymer. Theobtained porous, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 12, to thereby obtain a porous, crystallized polycarbonatehaving a weight average molecular weight of 28,300 (Mw/Mn=2.4).

EXAMPLE 18

An acetone slurry of porous, crystallized prepolymer obtained insubstantially the same manner as in Example 1 is dried to have anacetone content of 35% by weight. The resultant moist powder issubjected to granulation at about 40° C. by using a small size extruder(Pelleter BXKF-1 manufactured and sold by Fuji Powdal Co., Japan), toprepare a granular, crystallized prepolymer having a diameter of about 2mm and an average length of about 3 mm. The thus prepared granularcrystallized prepolymer is dried at 120° C. for 2 hours. The thusobtained granular prepolymer has a number average molecular weight of4,000, a molar ratio of terminal hydroxyl groups to terminalphenylcarbonate groups of 33/67, a specific surface area of 2.2 m² /g, acompressive break strength of 7 kgf/cm², and a crystallinity of 22%.

100 g of the granular crystallized prepolymer is placed in a glass-madegas flow type reactor of 50 mm in inner diameter having a glass filter(pore size: about 40-50 μm) attached to one end thereof. Nitrogen gas isintroduced into the reactor through the glass filter at a gas flow rateof 150 l(N.T.P.)/hr, and solid-state condensation polymerization isperformed under atmospheric pressure at 210° C. for 3 hours. As aresult, there is obtained a granular, crystallized polycarbonate havinga number average molecular weight of 12,100 and a crystallinity of 45%.The shape of the granular polycarbonate after the polymerization isnearly the same as that of the prepolymer before the polymerization.This means that the pulverization of the granules does not occur duringthe polymerization.

The granular, porous crystallized polycarbonate has a compressive breakstrength of 43 kgf/cm² and an equilibrium moisture content of 0.04%.This equilibrium moisture content is as low as about one-tenth of thatof a commercially available amorphous polycarbonate pellet.

EXAMPLE 19

An amorphous prepolymer having a number average molecular weight of3,800 and a molar ratio of terminal hydroxyl groups to terminal phenylcarbonate groups of 50/50, and containing no chlorine-containingcompound therein, which is prepared in substantially the same manner asin Example 1 except that the amount of diphenyl carbonate is changed to13 kg, is subjected to crystallization and granulation in substantiallythe same manner as in Example 18, to obtain a granular, porous,crystallized prepolymer of a cylindrical shape having a diameter ofabout 1 mm and a length of about 3 mm. The thus obtained granular,porous, crystallized prepolymer has a number average molecular weight of3,800, a molar ratio of terminal hydroxyl groups to terminal phenylcarbonate groups of 50/50, a specific surface

of 1.9 m² /g, a compressive break strength of 11 kgf cm², and acrystallinity of 25%.

100 g of the granular, porous, crystallized prepolymer is subjected tosolid-state condensation polymerization in substantially the same manneras in Example 18, except that the polymerization is conducted at 210° C.for 3 hours and then at 220° C. for 3 hours, thereby obtaining agranular, porous, crystallized polycarbonate.

The thus obtained granular, porous crystallized polycarbonate has anumber average molecular weight of 17,100 and a crystallinity of 51%.The shape of the granular, porous, crystallized polycarbonate after thepolymerization is nearly the same as that of the prepolymer before thepolymerization. This means that the pulverization of the granules doesnot occur. The granular, crystallized polycarbonate has a compressivebreak strength of 55 kgf/cm² and an equilibrium moisture content of0.04%.

COMPARATIVE EXAMPLE 5

The crystallized prepolymer as prepared in Comparative Example 1 issubjected to granulation in substantially the same manner as in Example18, to obtain a granular, crystallized prepolymer of a cylindrical shapehaving a diameter of about 2 mm and a length of about 3 mm. The obtainedgranular, crystallized prepolymer has a specific surface area of 0.04 m²/g.

The granular, crystallized prepolymer is subjected to solid-statecondensation polymerization in substantially the same manner as inExample 18, to obtain a polycarbonate having a number average molecularweight of 8,100. During the polymerization, any pulverization of thegranules does not occur.

EXAMPLE 20

Substantially the same moist powder as used in Example 18 is granulatedusing a compression molding machine under pressure of 1 tf/cm² to obtaina granular, porous, crystallized prepolymer of a cylindrical shapehaving a diameter of about 10 mm and a length of about 5 mm. Theobtained granular, porous, crystallized prepolymer is dried at 120° C.for 2 hours. Then, the granular, porous, crystallized prepolymer has anumber average molecular weight of 3,900, a molar ratio of terminalhydroxyl groups to terminal phenylcarbonate groups of 35/65, a specificsurface area of 2.1 m² /g, a compressive break strength of 26 kgf/cm²,and a crystallinity of 22%.

100 g of the granular, porous, crystallized prepolymer is subjected tosolid-state condensation polymerization in substantially the same manneras in Example 18 except that the polymerization is conducted at 220° C.for 2 hours, to obtain a granular, porous, crystallized polycarbonatehaving a number average molecular weight of 12,900 and a crystallinityof 40%. The shape of the granular, porous, crystallized polycarbonateafter the polymerization is nearly the same as that of the prepolymerbefore the polymerization. This means that the pulverization of thegranules does not occur. The granular, porous, crystallizedpolycarbonate has a compressive break strength of 120 kgf/cm².

EXAMPLES 21 TO 24

Amorphous prepolymers are individually prepared from bisphenol A,diphenyl carbonate and each of dihydroxyaryl compounds indicated inTable 1. Each of the amorphous prepolymers is subjected tocrystallization and pore formation, granulation, and solid-statecondensation polymerization, in substantially the same manner as inExample 18, to thereby obtain a granular, porous, crystallized, aromaticpolycarbonate. The properties of the porous, crystallized prepolymersand the polycarbonates are shown in Table 1. The crystallinity of eachof the porous, crystallized prepolymers is in the range of from 20 to38%. Any pulverization of the granules does not occur during thesolid-state condensation polymerization. The crystallinity of each ofthe granular, porous, crystallized polycarbonates obtained by thesolid-state condensation polymerization is in the range of from 40 to58%.

                                      TABLE 1                                     __________________________________________________________________________    Granular, crystallized prepolymer                                                                      Molar ratio of           Granular, crystallized                         (A) unit                                                                            terminal hy-             polycarbonate               Ex-                [mole]/                                                                             droxyl groups                                                                         Number                                                                              compressive                                                                          specific                                                                          Number                                                                              Compressive           am-                bisphenol                                                                           to terminal                                                                           average                                                                             break  surface                                                                           average                                                                             break                 ple                A unit                                                                              phenylcarbon-                                                                         molecular                                                                           strength                                                                             area                                                                              molecular                                                                           strength              No.                                                                              Dihydroxyaryl compound (A)                                                                    [mole]                                                                              nate groups                                                                           weight                                                                              (kgf/cm.sup.2)                                                                       (m.sup.2 /g)                                                                      weight                                                                              (kgf/cm.sup.2)        __________________________________________________________________________    21                                                                                ##STR20##      10/90 60/40   3,200 10.5   0.9 10,500                                                                              39                    22                                                                                ##STR21##      15/85 35/65   3,600 11.5   1.2 11,000                                                                              43                    23                                                                                ##STR22##       5/95 50/50   4,200  9.0   1.7 13,900                                                                              60                    24                                                                                ##STR23##      30/70 35/65   3,900 11.0   1.3 11,200                                                                              45                    __________________________________________________________________________

EXAMPLE 25

Pre-polymerization and crystallization using acetone are conducted insubstantially the same manner as in Example 1 except that 13.0 kg ofbisphenol A and 13.2 kg of diphenyl carbonate are employed, to obtain aporous, crystallized prepolymer having a number average molecular weightof 4,100, a molar ratio of terminal hydroxyl groups to terminal phenylcarbonate groups of 37/63, a crystallinity of 25%, and a specificsurface area of 1.1 m² /g. The thus obtained porous, crystallizedprepolymer is charged into a glass-made gas flow type reactor having aninner diameter of 15 mm and provided at its bottom with a glass filterhaving pores of about 40 to 50 μm in diameter. Then, solid-statecondensation polymerization is conducted at 210° C. for 2 hours underatmospheric pressure while introducing nitrogen gas into the reactorthrough the glass filter at a flow rate of 2.5 l(N.T.P.)/hr relative to2 g of the porous, crystallized prepolymer, thereby obtaining a porous,crystallized polycarbonate having a number average molecular weight of10,800.

Examples 26 to 28 and Comparative Examples 6 and 7

In each of these Examples and Comparative Examples, solid-statepolymerization is conducted in substantially the same manner as inExample 25, except that the flow rate of nitrogen gas, the reaction timeand the reaction temperature are individually changed to those indicatedin Table 2, to obtain porous, crystallized polycarbonates. The resultsare shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________            Flow rate                                                                              ratio of N.sub.2 *                                                                     Polymerization                                              of N.sub.2                                                                             to polymer                                                                             time    Temperature                                                                          Number average                               [liter (N.T.P)/hr]                                                                     [liter (N.T.P.)/hr]                                                                    [hr]    (°C.)                                                                         molecular weight                     __________________________________________________________________________    Example 26                                                                            0.4      0.20     3       220    10,600                               Example 27                                                                            1.3      0.65     3       210    11,000                               Example 28                                                                            8.0      4.0      3       210    12,000                               Comparative                                                                           0.1      0.05     8       210     7,500                               Example 6                                                                     Comparative**                                                                         16.0     8.0      3       210    12,100                               Example 7                                                                     __________________________________________________________________________     *Flow rate of N.sub.2 relative to 1 g of porous, crystallized prepolymer      **About 30% by weight of the charged prepolymer is entrained by nitrogen      gas and escapes out of the condensation polymerization system.   EXAMPLE      29

Pre-polymerization is conducted in substantially the same manner as inExample 1 except that 13.0 kg of bisphenol A and 13.3 kg of diphenylcarbonate are employed. The thus obtained amorphous prepolymer issubjected to crystallization and pore formation using acetone, followedby drying, in substantially the same manner as in Example 1, therebyobtaining a porous, crystallized prepolymer having a number averagemolecular weight of 4,100, a molar ratio of terminal hydroxyl groups toterminal phenylcarbonate groups of 35/65, a crystallinity of 25%, and aspecific surface area of 1.0 m² /g.

The porous, crystallized prepolymer (which has preliminarily been heatedto 180° C.) is subjected to solid-state condensation polymerization byusing a glass-made gas flow type reactor having an inner diameter of 15mm under conditions such that the pressure is maintained at atmosphericpressure while introducing, as an inert gas, nitrogen gas which issaturated with phenol at 0° C. (a partial pressure of phenol: 0.028mmHg), at a flow rate of 1.25 l (N.T.P.)/hr, per g of the porous,crystallized prepolymer, and the temperature is elevated from 180° C. to210° C. over a period of 30 minutes and then kept at 210° C. for 2.5hours, thereby obtaining a porous, crystallized polycarbonate having anumber average molecular weight of 11,400.

EXAMPLE 30 AND COMPARATIVE EXAMPLE 8

Substantially the same porous, crystallized prepolymer as used inExample 29 is subjected to solid-state condensation polymerization insubstantially the same manner as in Example 29 except that nitrogengases saturated with phenol respectively at 50° C. (Example 30) and at63° C. (Comparative Example 8) are individually employed as an inertgas, to obtain porous, crystallized polycarbonates. The partial pressureof phenol in the phenol-saturated nitrogen gas and the number averagemolecular weight of the resultant polycarbonate are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                 Partial pressure of                                                           phenol in phenol-                                                                         Number average                                                    saturated nitrogen                                                                        molecular weight                                                  (mmHg)      of polycarbonate                                         ______________________________________                                        Example 30 2.3           6,800                                                Compara-   5.7           4,300                                                tive                                                                          Example 8                                                                     ______________________________________                                    

As is apparent from Table 3, when the partial pressure of phenol in thephenol-saturated nitrogen gas is 2.3 mmHg, the number average molecularweight is promptly increased to 6,800, whereas when the partial pressureof phenol is 5.7 mmHg, the number average molecular weight is onlyslowly increased to 4,300 from 4,100 of the prepolymer.

EXAMPLE 31

Solid-state condensation polymerization is conducted in substantiallythe same manner as in Example 29 except that a granular, porouscrystallized prepolymer having a diameter of about 1 mm and a length offrom about 0.5 to about 2.0 cm, a number average molecular weight of3,980, a molar ratio of terminal hydroxyl groups to terminal phenylcarbonate groups of 36/64, a crystallinity of 25% and a specific surfacearea of 0.9 m² /g is employed, thereby obtaining a porous, crystallizedpolycarbonate having a number average molecular weight of 10,500.

EXAMPLE 32

The same granular, porous, crystallized polycarbonate as used in Example31 is subjected to solid-state condensation polymerization using amoving bed, gas flow type reactor made of SUS 304 steel having an innerdiameter of 15 cm and an effective length of 1 m and provided with anair pump and a gas-cooling device. The granular, porous crystallizedpolycarbonate is introduced into the reactor from its upper portion at arate of 1.2 kg/hr at a temperature of 210° C. for 20 hours whileintroducing nitrogen gas from the bottom portion of the reactor at aflow rate of 6 m³ (N.T.P.)/hour. Nitrogen gas containing phenol isdischarged from the reactor, cooled to 0° C. for liquefying and removingexcess phenol, and then heated to 210° C. The heated gas is thenreintroduced in the reactor. From 7 to 20 hours after the initiation ofthe operation, a granular, porous crystallized polycarbonate having anumber average molecular weight in the range of from 10,800 to 11,000 isrecovered from the bottom portion of the reactor at a rate of 1.2kg/hour. In this method, nitrogen gas is advantageously recycled.

The partial pressure of phenol of the recycled gas at a temperature of0° C. is 0.028 mmHg, which is calculated by the formula describedhereinbefore.

EXAMPLE 33

The same porous, crystallized aromatic polycarbonate as obtained inExample 1 is subjected to press molding at 30° C. under pressure of1,000 kgf/cm², to thereby obtain a pressed sheet (15 cm×15 cm×3 mm). Thesheet has an apparent density of 1.03 g/cm³ and a specific surface areaof 0.3 m² /g. Accordingly, the sheet, even after the press molding, isporous.

In a DSC chart of the thus obtained shaped article of porous,crystallized polycarbonate (pressed sheet), a peak representing thecrystalline melting point of the polycarbonate is observed at 271° C.The shaped article of porous, crystallized polycarbonate has acrystallinity of 45% and a compressive break strength of 25 kgf/cm² asmeasured using an Instron type universal tester.

EXAMPLE 34

A porous, crystallized polycarbonate having Mn of 13,000 as obtained inExample 1 is subjected to press molding at 200° C. under pressure of 500kgf/cm², to obtain a pressed sheet (15 cm×15 cm×3 mm). The thus obtainedshaped article of porous, crystallized polycarbonate (a pressed sheet)has an apparent density of 1.05 g/cm³ and a specific surface area of0.08 m² /g. The crystallized polycarbonate exhibits a peak of acrystalline melting point at 273° C. in a DSC chart thereof and has acrystallinity of 46% and a compressive-break strength of 150 kgf/cm² asmeasured using an Instron type universal tester.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron micrograph of the surface of the particleof porous, crystallized prepolymer of the present invention obtained inExample 1 (3060×magnification).

FIG. 2 is a scanning electron micrograph of the cross-section of theparticle of porous, crystallized prepolymer of the present inventionobtained in Example 1, which has been broken with forceps(1020×magnification).

FIG. 3 is a scanning electron micrograph of the amorphous prepolymer (I)obtained by pre-polymerization in Example 1 (4400×magnification).

FIG. 4 is a scanning electron micrograph of the surface of the particleof porous, crystallized prepolymer obtained in Example 2(1020×magnification).

FIG. 5 is a scanning electron micrograph of a portion of the particleshown in FIG. 4, which is taken with higher magnification(3060×magnification).

FIG. 6 is a scanning electron micrograph of a portion of the particleshown in FIG. 5, which is taken with higher magnification(6020×magnification).

FIG. 7 is a scanning electron micrograph of the particle of porous,crystallized prepolymer of the present invention obtained in Example 9(3060×magnification).

FIG. 8 is a scanning electron micrograph of a portion of the particleshown in FIG. 7, which is taken with higher magnification(6020×magnification).

FIG. 9 is a DSC chart of the porous, crystallized, polycarbonate of thepresent invention obtained in Example 1.

FIG. 10 and FIG. 11 show examples of X-ray diffraction patterns of aprepolymer before being subjected to crystallization and after beingsubjected to crystallization, respectively.

INDUSTRIAL APPLICABILITY

The porous, crystallized, aromatic polycarbonate prepolymer of thepresent invention can readily be converted by solid-state condensationpolymerization to a porous, crystallized, aromatic polycarbonate. Theporous, crystallized, aromatic polycarbonate of the present inventioncan readily be molded to obtain a shaped, porous, crystallizedpolycarbonate. The porous, crystallized, aromatic polycarbonate and theshaped, porous, crystallized polycarbonate of the present invention haveexcellent heat resistance and solvent resistance and exhibitadvantageously low water absorption so that these are suited for use asa filter material, an adsorbent or the like. The porous, crystallized,aromatic polycarbonate and the shaped, porous, crystallizedpolycarbonate of the present invention can also readily be molded by amelt process into an article useful as engineering plastics, such as anoptical element and an electronic component.

The conventional phosgene process has drawbacks in thatchlorine-containing compounds attributed to phosgene as a raw materialand methylene chloride as a solvent inevitably remain in the finalpolycarbonate product despite complicated, costly steps for removingthem, and in that it is difficult to obtain a polycarbonate having anultra-high molecular weight. On the other hand, the conventionaltransesterification process also has drawbacks in that a highlyexpensive reactor usable under extremely high temperature and vacuumconditions is necessary, and that it is difficult to performpolymerization without thermal degradation and to obtain a polycarbonatehaving an ultra-high molecular weight.

By contrast, the prepolymer and the polycarbonate of the presentinvention are free from the above-mentioned drawbacks of the prior artprocesses. Moreover, in the present invention, a reactive hydroxyl groupcan readily be introduced in an aromatic polycarbonate.

Accordingly, the porous, crystallized, aromatic polycarbonateprepolymers and porous, crystallized aromatic polycarbonates of thepresent invention as well as the production methods of the presentinvention, can advantageously be utilized, especially in the field ofengineering plastics which have been rising in importance.

We claim:
 1. A porous, crystallized, aromatic polycarbonate prepolymercomprising recurring aromatic carbonate units and terminal hydroxyl andaryl carbonate groups, wherein the molar ratio of the terminal hydroxylgroups to the terminal aryl carbonate groups is from 5/95 to 95/5, andhaving a number average molecular weight of from 1,000 to 15,000, aspecific surface area of at least 0.2 m² /g and a crystallinity of atleast 5%.
 2. A prepolymer according to claim 1, wherein the specificsurface area of the prepolymer is at least 0.5 m² /g.
 3. A prepolymeraccording to claim 1, wherein the crystallinity of the prepolymer is notgreater than 55%.
 4. A prepolymer according to claim 1, wherein theratio of the terminal hydroxyl groups to the terminal aryl carbonategroups is from 10/90 to 90/10.
 5. A prepolymer according to any one ofclaims 1 to 4, which is in powder form.
 6. A prepolymer according to anyone of claims 1 to 4, which is in agglomerated powder form.
 7. Aprepolymer according to any one of claims 1 to 4, which is in granularform.
 8. A prepolymer according to claim 7, which has a compressivebreak strength of at least 5 kgf/cm².
 9. A prepolymer according to anyone of claims 1 to 4, which is for use as a prepolymer to be subjectedto solid-state condensation polymerization.
 10. A prepolymer accordingto claim 5, which is for use as a prepolymer to be subjected tosolid-state condensation polymerization.
 11. A prepolymer according toclaim 6, which is for use as a prepolymer to be subjected to solid-statecondensation polymerization.
 12. A prepolymer according to claim 7,which is for use as a prepolymer to be subjected to solid-statecondensation polymerization.
 13. A prepolymer according to claim 8,which is for use as a prepolymer to be subjected to solid-statecondensation polymerization.
 14. A method for producing a powder form ofporous, crystallized, aromatic polycarbonate prepolymer, which comprisestreating an amorphous aromatic polycarbonate prepolymer with solventunder sufficient shearing force to crystallize and render porous saidamorphous aromatic polycarbonate prepolymer,said amorphous aromaticpolycarbonate prepolymer comprising recurring carbonate units andterminal hydroxyl and aryl carbonate groups, wherein the molar ratio ofthe terminal hydroxyl groups to the terminal aryl carbonate groups isfrom 5/95 to 95/5, and having a number average molecular weight of 1,000to 15,000, said shearing force being sufficient to cause the resultantpowdery, porous, crystallized, aromatic polycarbonate prepolymer to havean average particle diameter of 250 μm or less.
 15. A method forproducing an agglomerated powder form of porous, crystallized aromaticpolycarbonate prepolymer, which comprises applying sufficient pressureor heat to particles of a powder form of porous, crystallized aromaticpolycarbonate prepolymer to cause the particles to be cohered,theprepolymer of said powder form of prepolymer being prepolymer accordingto claim
 1. 16. A method according to claim 15, wherein the specificsurface area of the powder form of prepolymer is at least 0.5 m² /g. 17.A method according to claim 15, wherein the crystallinity of the powderform of prepolymer is not greater than 55%.
 18. A method for producing agranular form of porous, crystallized, aromatic polycarbonateprepolymer, which comprises granulating a powder form or an agglomeratedpowder form of porous, crystallized, aromatic polycarbonateprepolymer,the prepolymer of said powder form or of said agglomeratedpowder form of prepolymer is prepolymer according to claim
 1. 19. Amethod according to claim 18, wherein the specific surface area of thepowder form or of the agglomerated powder form of prepolymer is at least0.5 m² /g.
 20. A method according to claim 18, wherein the crystallinityof the powder form or of the agglomerated powder form of prepolymer isnot greater than 55%.
 21. A method according to claim 18, 19 or 20,wherein the granulation of the powder form or of the agglomerated powderform of prepolymer is performed by extrusion-granulation or bycompression-granulation.
 22. A porous crystallized aromaticpolycarbonate prepolymer which is at least substantially the same asthat produced by a method of one of claims 14 to 17 and 18 to
 20. 23. Aporous crystallized aromatic polycarbonate prepolymer which is at leastsubstantially the same as that produced by a method of claim 21.